Honestly..I don't understand why people find it outside of the realm of possibility that an extra set of characters will be available for unlock along with the release of the Wii-U version. These characters WOULD NOT be exclusive to the Wii-U, so please for the love of god stop using the argument about the rosters being the same. They would be.
The way I see it..these characters would be unlocked either on star-up (initially available), or through a game mode only on the Wii-U version. After sometime (either a few days to 2 weeks I would guess) after people have unlocked them, the fear off blowing spoilers would be significantly diminished and these characters would be available for download as DLC. If not DLC first, then simply Wii-U connectivity and transferring the character data. Obviously, any copy of the Wii-U version will work..so if you don't have a Wii-U, all you have to do is find someone who has the characters and lets you connect to their Wii-U and get it from them. I wouldn't be surprised if they expect you to do it that way AT FIRST, and then eventually just release the content as DLC.
For all of you rambling about Sakurai being against DLC, learn to google.
"Sakurai on how Smash Bros. Wii U/3DS came to be, not opposed to DLC, patching, why Villager/Trainer are in, more" i cant post links so throw that in google
Furthermore, for the people who want to argue that Nintendo wont force people to buy both/people cant afford both so it isn't fair....just calm down and continue reading. First, keep in mind that the 3DS version is already out..2-4 months before the release of the Wii-U version. There are likely many reasons for this, one of them being a nod to the fact that the system is cheaper (the 3ds and game together is cheaper than a WIi-U system alone). Regardless of what Sakurai and others might say, everyone understands consciously or not that the Wii-U version is the "main" version off the two. If people are home or at tournaments, or simply have the in the moment choice of playing Smash on either a 3ds or Wii-U, the Wii-U version will be picked nearly every time (if you want to refute that, go ahead but realize you're the hard minority). I am convinced the 3ds copy of the game is a sort of...version 1.0 appetizer as we wait for the main course come winter. $40 for the game isn't going to burn a hole in anyone's pocket, and additionally if you don't have a 3ds and can't wait for the Wii-U version to come out, you can get the two together for $200 give or take..roughly half the price of getting a wii-u and smash together (doing it the other way around).
Second, I say main in quotes because, in essence, the games are equal. They will offer the same characters, same mechanics and items, ability for online play, and game change/feature updates. So yes, they are equal. However, the games are paternal twins. They share the same DNA, but they are presented differently from eachother..and the Wii-U version is the older brother. We already know FOR FACT the the Wii-U version will have more game modes (or modes the 3ds doesn't offfer) as well as completely different stages. People overlook this..especially the stages and they are extremely important to look at. Take a look
"super smash bros 3ds stages mariowiki" throw into google
What you will hopefully notice is of the FEWER stages known to be on the Wii-U, many of the are actually designed as a competitive arena, where as the 3ds stages have a much more casual appeal (many scrollers, walk-offs, etc). Now, I'm not saying that all of the 3ds stages are casual/unusable..no. There are definitely stages that can be used in a competitive way. However the large majority of stages (both old included and newly designed) are very rng based or scrolly or have no bottoms. I don't know the details of each stage known so far on the WIi-U, but you can check out the link and see for yourself that most of the arenas have a much more neutral design, offering flat ground, with platfforms, and area to die from the top, sides and bottom. The obvious reason is that the Wii-U version wants to offer a more competitve-esk feel to it. Or rather, to have the ability to be played more competitively and have a players individual skill the opportunity to shine. Nintendo and Sakurai understand that players want and should have the opportunity to take the game about as far as they want it. Maybe the game won't have the skill ceiling of melee, but the main factors that make up the meta were unintended and simply clever abuse of buggy game mechanics. I'm certain Sakurai wants to develop the game such that skill can still be earned and respected within the use of the intended mechanics of the game. Much like the early days of Ken when he was winning tourny's without even knowing how to wavedash. My point is, the console has, and for the time being, will always be THE way to play competitively. Not only with smash, but other fighters too. (see gamecube controller release for wii-u too..if that's not a nod then I don't know what is).
SO, so far we have 1)the 3ds is cheaper and more accessible 2) the wii-u version offers more things and is more competitively grounded
Third, Nintendo wants people to own Wii-U's. I mean..thats the end goal right? To sell systems and get you playing games on them. It's not really fair to make customers spend nearly $600 just to play smash (buying both systems and both copies). That's why they offer you the alternative of having a cheaper version on the 3ds, which is good enough for many players and casuals and children, or having a more expensive copy on the Wii-U, which will be the desire of everyone who truly supports, cares, and enjoys the series among those who already own Wii-U's. That's also why it makes sense to separate the releases of the two games. If they were released simultaneously, people would be far, far more likely to only pick up 1 copy of the game depending on what system they have, especially when the connectivity doesn't really offer much at the moment. Splitting the releases offers Nintendo a lot as far as added revenue for doing nothing on their end. By splitting the releases, thos who have Wii-U's will likely buy/have bought already 3ds's just to play the game..not only spending an extra $40 for a not as good version of the game but also spending upwards of $150 on a 3ds to fill the void for a few months. Now these cases might not be the majority of players, but it certainly does pertain to a few. The main goal is to get people to buy the 3ds game now who don't have Wii-U's..play it, enjoy it, and get hyped with the Wii-U version comes so they spend an extra boatload of cash. The best way to milk the money is to separate the releases. There's no denying it.
Knowing this, it makes complete and total sense that Nintendo needs/is making Sakurai do SOMETHING to hype the Wii-U release of the game. Personally, a soundtrack mode and a few different stages isn't enough for me to be willing to shell out 400 for a Wii-U and the game to play it often enough to warrant buying the system and getting good. Especially when games like Project M exist that have a deep meta and updates and a dev team that listens well. It would be much more in my favor to spend half the money, buy a 3ds and smash 4, and leave it at that.
So how are they going to build hype? I would say the easiest way is to provide more fan service..and how better to do it than in the form of more characters? Which brings me to point 4.
Everyone has seen the character select screen on the 3ds *** version of the game either through pics or twitch stream. With the full grid design, it's clear that there could fit 5 more character portraits to make 6 rows of 9 and completely fill the screen. Now obviously 5 characters is a lot to add, But speaking STRICTLY from a symmetry standpoint, it makes no sense to me that they would choose to adopt that particular style select screen and leave it so open towards the end (especially the 2nd to last row). If this was the max number of characters and whats done is done, it's designed with bad taste. And with the sleek appearance of the simple menus, it doesn't make sense.
Furthermore, part of the fun of the other modes is the fact that you needed to do them in order to unlock more characters. That's part of the fun. If the Wii-U verson is going to have different modes, including ones with boss battles..why they hell am I going to play it if not to unlock something? Simply for collecting more trophies? I certainly hope no one would spend 400 just to grab an extra 50 character trophies. So in that respect, new modes doesn't guarantee new characters, but it certainly makes playing the modes 10x more compelling. And they know this.
Another thing..Sakurai and Nintendo know how badly players want certain characters to be in the game. In the interview link above, Sakurai stated he wants to put the maximum content for the players (when asked about new characters). He also stated that he had already collected the data on what people wanted, which likely came from around 2010-2012. Polls will show you the top 5 most requested new characters during that time period..and all are missing from the current roster (except Megaman!!). Issac (golden sun), Ridly (metroid), and King K. Rool (donkey kong). Ridly is obviously in the game in some shape or form, but no one really knows how for certain. I'm not going to try and speculate who the characters being added in are, but I would think that it would likely be at least one of these 3.
TLDR: DLC is a viable possibility and new characters unlocked with the Wii-U release are not guaranteed, but are likely.