Resident Evil 5 is an excellent game on the Xbox 360, the only system I've played it on.
That said, I would be interested to see how a Wii adaptation would be handled. Wii doesn't have the horsepower to handle tons of AI Zombies (oxymoron?) like the 360 and PS3 do, but RE5 didn't have hordes on the lower difficulty levels.
By trimming down on the polys and environmental details, I'm sure a Wii version could be done. Heck, RE4 looks fine on Wii, and RE5 is clearly based upon it....
The question is, if RE5 DOES come to Wii, will they leave in the extremely awesome Online Co-op feature?