To me, the ballot would be a huge misfire on Nintendo's part if they only add 1-2 characters from its early life and then go "btw the rest of the votes are just consideration for 5mash." The ballot clearly states at the top "Do you want your favorite video-game character to join the battle in Super Smash Bros. for Nintendo 3DS/Wii U?" Not "Do you want your favorite video game character to be in a future Smash game?" If they weren't going to have payoff for the whole six months, why run it that long?
That's the beauty of language, things can easily be framed in one manner but they can take on multiple meanings, have hidden meanings etc. They would never publicly say "lol we only are using 2 and the rest we will save for possibly another day". I imagine it was run for the length it is due to the fact if it was any shorter people would demand "results" or characters to be released based on that in a much shorter timeframe then they could actually produce ballot characters *and* the current DLC we had so far. 6 months is more then enough time to get results and at least start work so when the ballot does end they can release it within a reasonable timeframe afterwards.
Think about it this way, when October comes around and Sakurai does a special video or something to announced the winners and goes "As a result of your votes the following characters will be joining the battle, X, Y and Z" people will be sad that their individual favourites weren't picked but no-one is going to go "oh man this is lame why didn't they put 6+ characters in?" they will be more invested into who did get in and the fact they had a voice at all. This is the first time fans in the west have actively been able to contribute to suggestions as previously its only been japan that had a direct fan poll for suggestions.
For those who don't get in via the Ballot, Should they ban them from ever being in any future smash games because of some vague interpretation? Of course not, they'd naturally be considered for any future games and DLC. Fans don't need to know every single aspect of development and production.
What about the 3DS version,the screen is full
Since every player has their own screen they aren't restricted to the same design principles as the Wii U version, so as suggested already arrows and other redesigns not practical for the Wii U would be fine for 3DS.