Well they won't take Wii play away from the Wii remote, at least i wouldn't have thought so, i think when they do add more remote bundles the Wiiplay will remain, and still sell at least 1/3 - 1/2 of what it is doing now until late in the consoles life, which would still be amazing numbers and still make the top 10 (whether it is pushed out by later games i can't guess)
According to Miyamoto Wii sports 2 is not even on the table at the moment, If it does happen it is a long way away, (maybe for christmas 2009 they will take out Wii sports from the Western bundle and add Wii sports 2 (also seperately selling wii sports as a budget title and 2 as a full price)....if that does happen and the Wii is still selling phenomenally then yes it could.
Now that i rethink, MarioKart might actually have the most sales out of the big3 because it appeals more to anyone, Smash and Galaxy are being hyped in the gaming community so much i dismissed the fact that MK:DD was the best selling GC game.
i would still put Galaxy at 15 million at least though....SmashBros maybe about the same, but as melee only sold 6.58 i am not sure.
Animal Crossing?....that sounds like a long shot to me, remember each time a new game enters the top 10 it ups the bar for the next one to make it, so a currently unannounced game would have to sell 18 million to make it due at least 3 of the four games i mentioned (in bold on OP) will manage that.
The above statement pretty much means Halo3/4 and Gears2 have no chance of making it....i think by the end of this generation there will be at least 4 new games in the top 10, meaning 4 games with sales of > 18.14M. it think it could even be up to 6 new games (>23.10) and at least 5 more games will have entered the top 10 but been pushed back out.....Like Erik implied, the top 40 is going to be redefined this generation--possibly no more games with less than 10 million sales.
p.s. Wii sports online would be incredible, that's what Wii sports 2 should be, Tennis/Bowling/Boxing plus two other sports (lose golf/baseball)