I know we just got three characters at once from the Smash direct but I'm pretty sure we'll get at least one or two before the poll ends in October...
I want to confidently say that Wolf will be next (but we all said that when Lucas was announced and we ended up getting two characters before him with still no confirmation)...he'll most definitely be added eventually because there really isn't anything holding him back especially with him being confirmed in the new Star Fox game...but that still raises the question...if not Wolf, then who?
When it comes to veterans the next two popular picks are Snake and Ice Climbers who were excluded because of Third Parties shenanigans and hardware limitations respectively...
Konami's current situation has the company deteriorating, which may be a good or bad thing if you think about it...Nintendo may pick up the Metal Gear IP if things really go south for the company which would give Snake 1st Party privileges (this is just one highly unlikely scenario mind you)...as for the Ice Climbers it's really a matter if they'll get hardware limitations sorted out or not on the 3DS...
Other vets aren't really all that heavily demanded and if they were to be added it would most likely be later on down the line after the ballot closes...
As for newcomers?....prffft...Good Luck predicting that one......because when DLC was officially announced who would've guessed that Ryu of all people would've been the first DLC newcomer? Frikken RYU!!
But based on current observations...
King K Rool is likely leading the Ballot, with characters Isaac, Bandana Dee, Inklings, Captain Toad,
Ridley, Dixie Kong, etc. behind him...but those are just the obvious choices...
Dixie Kong, Toon Zelda/Toon Sheik, Pra_mai (possibily Plusle and Minun) were all intended in brawl and so were Dr. Mario, Mewtwo, and Roy, the latter three already are available in game in that order...that's another thing to take note of, although each of the three added from the forbidden 7 were all veterans from melee so they had more incentive to be added than the others...
Then again with Ryu being added as well as Virtua Fighter and Tekken Mii costumes shows that Capcom, Sega and Namco are still adding more content into Smash and may very well keep adding some of their own stuff in the future...Possible second Sega and Namco character coming?...Ryu's addition broke the fan-made 'one per third party' rule, as well as contradicted the statement Sakurai has made in regards to Fighting Game characters, so it isn't so
; but as of now it's really a matter of just waiting it out until the next fighter is revealed which will most likely be August...(or sooner in a surprise Direct, but that's just wishful thinking hehe...or is it?)