Now that we've cleared up that it is possible to fit everything on a Wii disk the only reason why the Wii cannot play the same games that the 360/PS3 can is purely down to processing power. If the Wii can't run a game engine then the game has to be cut down to allow it to run.
COD:WAW is a good example, it used the same engine as the 360/PS3 versions but the cost of running the engine was that some of the content had to be left out (either that or lazy development).
RE:5's engine doesn't look much improved over RE:4 to me, the only real change being online/co-op modes. They could just reuse the RE:4 engine and cut some content to make a quick and easy Wii specific RE:5.
Now people may be against an altered Wii version but it could actually make for a better game. RE:5 lost any 'survival horror' aspect and ended up being just another 3rd person action shooter. RE:4 was more 'survival action' with a bit of horror, so changing RE:5 to something more like RE:4 could be a good thing.
The Wii already has the best RE:4 version, archives coming out and the Wii exclusive rail shooters (as well as playing the NGC games) so if they did reformat RE:5 over to the Wii then it could end up as being the best system for the entire franchise.
Wii games - SMG, Zelda TP, Mario Kart, SSBB, Wii Sports, Wii Play, Endless Ocean, Blue World, Wii Fit, Super Monkeyball, Rogue Trooper, Shaun White, NMH, NMH2, GH: WT, Aerosmith, Zack&Wiki, Okami, RE4, Force Unleashed, Clone Wars, Scarface, PES, Tenchu, Trauma Centre NB, Madworld, Rune Factory, Wii Sports Resort, Metroid Prime Trilogy, Muramasa, COD Reflex, Obscure, Silent Hill, Rabbids Go Home, NSMB, Bully, Tatsunoko vs Capcom, Red Steel 2, Monster Hunter Tri
If they were to making anything remotely close to a RE4 or RE5, they'd have to start from scratch and build up the game with one of the engines they have available. There's really no way for them to port it over at it's current state.