I think it's a possibility. I believe that Nintendo will definitely put more Wii Plays out into the market then Wiimotes, and since people seem to really want more Wiimotes, that sales are going to continue to stay high.

What do you think?

Well right now it sits at 46th best selling game of all time. While it is doing well, I think it will slow down because of 2 main reasons. 1. Games by nature slow in sales 2. More Wii branded games are coming out soon which will divert some sales towards those games.

I think a good part of why Wii Play is so popular is because its in the Wii franchise (WiiSports, WiiPlay, WiiMusic, WiiFit). Once WiiFit and WiiMusic come out, WiiPlay wont be as popular. Right now its just the only choice. I do think, however, it will eclipse the top 15 with around 15 million copies sold by the end of this generation of gaming.

I think Nintendo will release a whole new game that comes with a wiimote. Hopefully it will be something completely different from wiisports/play.

Nintendo already released BBA as a wiimote bundle DownUnder. Maybe that will spread. Maybe Wii Music will be bundled with a wiimote (or even a Nunchuk) in 2008. Either way, I think Nintendo may release another bundle as Damkira said. I have 3 wiimotes and would like another one but am holding off for just that senario.

Oh, and if any Wii games was to become the best selling game ever, it would be Wii Sports. 

They could sell it seperately for $19, would be interesting.

I don't think WiiPlay has a chance in hell of moving more units than WiiSports, so it's basically impossible for it to be number one of all-time. Now WiiSports might be able to beat SMB...

Of course, all Wii owners are buying Wii play. It's simple, and moderately fun, but if history is made, and Play becomes the best selling game of all time, then I will be so dissapointed. Wii play is just a tech demo for the Wii-remote. I can't consider it a complete game.

I have no clue how the attach rates for second controllers are, but assuming that one third of the Wii owners want a second Wiimote, that means that 120 million Wiis must be sold that Wii Play will beat SMB.

Looking at it like this, it is possible. But as soon as Nintendo releases another game bundled with a Wiimote for such a price, Wii Play's sales will drop drastically. Also, Wii Sports will always sell more as Wii Play as long as both bundles are not changed, so Wii Play has a chance at beating SMB, but not at beating Wii Sports.

if anygame will beat smb it will be wiisports

But WiiSports comes with every wii sold (apart from Japan ofc), so its different.

I would be slightly dissapointed if Wiiplay became the best selling "game" of all time, as its hardly a game, its more like a freebie tbh.