This will never happen. You notice how pretty much ALL of the big A-List games aren't on the Wii? They all use hi-def graphics these days and the Wii just unfortunately can't compete on the same level, and RE5 is going to be extremely graphically intense, they would never release two hi-def versions and one worse-looking version. The Wii comes out with games that play to it's strengths, not ones that embarrassingly point out its flaws.
Get a 360 AND a Wii and enjoy the best of both worlds.