I would much rather play this game on the Wii than on the PSP. The MGS3 engine on the PS2 looks far better than the PSP engine, and the Wii is more powerful than both by a good margin. Plus the analog stick on the Wii is more more comfy and there's many more game play oppurtunities with Wii Motion Plus.
If Monster Hunter 3 is a hit (being the first real "core" hit title for Wii in Japan) and Wii sales in Japan rise, I hope Konami will consider it.
If the 360-PS3 get to share games, there's no reason the Wii shouldn't get its own version of games like MGS: Peace Walker or Final Fantasy Dissidia or Kingdom Hearts: Birth By Sleep at all.