Maybe this is just blind optimism talking, but here's how I hope things pan out as far as the DLC situation is concerned. If Mewtwo and Lucas are any indication, DLC characters might be released every two months, at least until October and the end of the poll. I realize that two examples don't make a pattern, but I'm thinking that at E3 (which is in mid-June), we'll get an announcement for Wolf as DLC, who's due out in August. I'm just figuring this because we're almost definitely going to be getting more information on Star Fox at E3 (since, as far as we know, it's still coming out this year), and if Lucas is being brought back, it seems pretty likely that Wolf is planned for some point down the line.
Assuming that keeps up, it seems like there would be one more DLC announcement in August before the poll ends in October, in order to get people excited for the final stretch. Again, this is purely optimism on my part - I don't have any clue how many DLC characters we'll be getting, or if anyone will even be announced at E3. However, if it does work out like that, and somebody gets announced in August, I feel like that would be a good time to show Snake. Metal Gear Solid V's release is right around the corner, and if my guess is right and they do reveal Wolf at E3, it would seem to indicate that they'd be sticking with veterans before the poll ends.
Assuming that they can't work around the 3DS's limitations, Ice Climbers wouldn't be an option, and there isn't really a huge outcry for Squirtle, Ivysaur, Pichu, or Young Link, at least from what I've seen (if there is, I apologize; I just haven't seen a whole lot of campaigning for their inclusion or complaints about their absence). I just figure that, if Wolf gets announced at E3, it seems like Snake would most likely be the next choice. Does this make any sense, or am I just sounding like a crazy person?
tl:dr, this is what I'm thinking might happen:
-Lucas comes out in June (around E3), Wolf gets announced at E3
-Wolf comes out in August, Snake gets announced around that time to keep up excitement before the poll ends (other cut veterans wouldn't get as much of a reaction)
-Snake comes out in October; poll ends and we get a newcomer as DLC much further down the line