Actually... it could be Krystal. Bear with me on the following, as some of it might seem long-winded. However, it remains interestingly possible.
Firstly, I established that Star Fox 3D was released on July 14th, 2011, right? It was released in Japan that day, not the U.S.
Why is that significant? Well, Sakurai released veterans on multiple anniversaries/release dates of certain games. Most of these dates (in fact, all that I can remember) were the Japanese anniversaries/release dates. King DeDeDe is one example, and Yoshi was going to be another (but was held for the direct due to fine-tuning changes, which eventually led to the speculation of changes in Metaknight and Ganondorf, but that's another topic). Diddy Kong, I believe, is another.
Here's the thing: the Japanese anniversary of Star Fox 64 3D on July 14th could hint to the veteran inclusion of the newcomer trailer, for most (perhaps all, even) of the anniversary-related characters were veterans. Also, how many franchises are starving of content in the new Smash Brothers so far? Besides Mother/Earthbound, I can only really think of Star Fox...
Not only that, but there's the curious spacing of the portraits of veterans and newcomers on the Smash home website. The most common pattern (if you want to call it a pattern, a pattern that repeated 4 times successfully) is: Veteran, Veteran, Veteran, Newcomer (and it squares up nicely on the website, but... details, who really cares?). I realize that this isn't consistent through the entirety of the website, but it has only been disrupted by both E3's. Yes, this pattern survived through the Smash Direct, and that was considered big.
Why could this matter? Besides, this would mean that we could get Falco, Wolf, Krystal; Veteran, Veteran, Newcomer (thus not conforming to the pattern itself). Ladies and gentlemen, I'd like to point you to Nintendo's sponsorship of Evo. Yes, Evo is happening this weekend. Nintendo could reveal a veteran there, easily (or the Monday pic of the day, following Evo). Captain Falcon hype, anyone? (Probably won't happen, but this is all theoretical, so don't bash me for "grasping for straws", as I'm well aware that I could very well be. Like I said before, sometime's it's fun to extend hypothesis and embrace the possibilities through speculation, but that's just me). Thus, with a veteran reveal at Evo, plus the remaining Star Fox cast (plus Krystal) on Monday, the pattern would be restored: Veteran, Veteran, Veteran, Newcomer.
Honestly, the point above doesn't really matter one way or another, but it is interesting. The smash site will live if this doesn't turn out to be a stock pattern, and the possibility of Krystal being revealed on Monday certainly doesn't hinge on this point either. I personally think that having four newcomer portraits back-to-back, while roughly eleven veterans have yet to be shown, would be odd, but that's my opinion.
There is another more interesting point, though. The next point is more hypothetical than the previous ones (but it makes more sense than the previous point all together).
Many of us are assuming Sakurai is well aware of the Gematsu leak, right? And because of Rosalina, I'm sure that it's a safe bet there are other characters Gematsu wasn't aware of (or, knowingly didn't leak on purpose, but that's a topic I'm reserving for a later date...) that have yet to be revealed. E3 just confirmed three additional Gematsu characters. I would like to think, that if this is possible, Sakurai would throw in another curve ball to surprise us, somewhere.
This, and Monolith Soft, while they retweeted Sakurai's post, have retweeted many Smash-related things in the past few months, so I'm not convinced that it's sure-fire evidence for Shulk. Sure, it's the writer this time around, but I'm still not entirely convinced.
But there's something else to this point:
I have a question to all who read this post. How aware is Sakurai about the flak that the Star Fox franchise has received due to the semi-clone feel of the characters and their literal clones-for-Final-Smashes in Brawl?
I'm actually surprised that I haven't seen this brought up before. This is the next Smash Brothers game! Do we really think that Sakurai, who's probably no doubt aware of the flak that the Star Fox franchise has received in Brawl, is going to repeat the same mistake, or neglect the franchise from a chance to finally prove itself capable of producing a fighter that can truly be unique or different than the other Star Fox characters? And again, they can show us all of the new final smashes together, to showcase and clarify how different they are.
I can see it now:
Masahiro Sakurai
"Look Ma, no multiple land masters!"
To me, this is why it makes sense for Sakurai to release Krystal along with Falco and Wolf, instead of Krystal being DLC. No other franchise (save for certain characters, i.e. Ganondorf, but this is referring to whole franchises) on the Smash roster has some important change that is needed, and needed to be clarified. Along the production of Smash 4, Sakurai has made clear the changes made to certain characters from the past iterations of Smash. Why would he miss this opportunity to capitalize on clarifying the changes to a franchise in Smash Brothers that, easily more than every other franchise on the roster, desperately needs a change to be clarified to the Smash audience? It almost makes no sense not to. Besides, this is an excellent time to finally show us a stage or two for Star Fox! On-ground Sauria, anyone? *Cough Cough*
If the change isn't made, and clarified, I predict the Star Fox franchise to continue receiving flak regarding representation and character feel. That would be incredibly unfortunate.
Besides, I think we've forgotten about the way Charizard was revealed in the Smash Direct. Firstly, he's the only veteran to be revealed, so far, in a newcomer trailer. There was a reason, though. Sakurai used the newcomer trailer of Greninja to punctuate the clarification that Charizard is no longer with the Pokemon Trainer. To me, it seems that veterans might only become included in a newcomer trailer if there is a change that is needed to be clarified within said trailer. This method maximizes the effect of the change through clarification on the audience, mainly because people are now able to associate said change with the trailer and/or newcomer (basic psychology). I think the Star Fox veterans are in need of a clarified change regarding move-sets and Final Smashes, due to the mostly negative reception the franchise received in Brawl. A great way to punctuate such a change would be for Krystal to spearhead it.
Anyways, these were a couple thoughts of mine. What do you guys think? Personally, I'm not expecting anyone specific. I'll wait and see who it is on Monday. I just thought some of these points could be interesting.