To be honest with you, I could see a version of Burnout 5 more akin to that which we've seen on the xbox or ps2.
Unfortunately the Wii is just not a graphical powerhouse compared to it's next gen counterparts.
Another unfortunate thing is that the wiimote is all fun for action and such but for driving it's kind of a pain in the butt. It would be cool however to be able to shake the controller during a trademark burnout crash to cause more damage and effects onscreen.
The biggest reason we may not see a wii version of the same game is that it would look absolutely terrible in comparison, this is why we are seeing a different spiderman 3 on the wii as oposed to the xbox360 and PS3.
I'm sure we'll see some sort of burnout make it's way to the wii in time however, just don't be expecting too similar of a version as the other two systems, it's just not worth the downgrade.