Mmmm...I don't know the code of MW3, but the hosting problem may not be as easy to fix, at least in a reasonably sized patch. I don't think is just the way shooting and internet speed is managed as probably was with lag-shooting.
Being a host will always require more RAM than other non-hosting Wiis, the host basically gathers and double check all the match stats, and decides who dies in a face to face fight. The game wasn't polished enough. Maybe even the size of the maps and the details take over a lot of Wii resources already, so adding hosting to that may make things worst. For example there is no map in which I feel there is no frame rate issues when I'm not hosting, add to that being host, it of course it will get worst.
I think more fixable little problems are the spawn system, the matchmaking system, fix some glitches, lowering down the power of some weapons (example; reducing the effectiveness akimbos at mid range, and quickscope), and increasing the power of some killstreaks like the choppers and turrets, adding a lil more effective radius for the grenades, increasing the length of UAV, not allow assassin pro to avoid the Advanced UAV as it was in BLOPS.
I bet most of the things mentioned above involve just changing a number or two en the code, easily patchable. Like "effective radius=3", "range=9", etc.
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