The fighting polygon team was not "replaced" in Melee, they were just upgraded to wireframes due to the more powerful hardware. It's the same basic concept, and fully expect them to keep it that way in Brawl.
That's where you're wrong. The Wire Frames are completely different characters. Yes, the concept was similar, but they're completely different. It's not the hardware itself. It's the fact that "Frames" are used instead of "Polygons" for characters, so they went with that instead.
Since there are 26 overall characters in Melee, making 26 different Wire Frames would take forever and be a giant mess. So they chose two powerhouses and created a Frame version of each. Zelda literally is the most powerful amongst the females. Falcon was also the most powerful of the non-unlockables. They went with them, used the classic cloneage, took their original frame, changed their color to blue itself, added the Smash symbol, make some slight move changes, and voila, the "Fighting Wire Frames" were born. Although it doesn't sound simple, it mostly is. Not much effort was done to make them, but neither were the clones.
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Now, as for the topic onhand. I'd rather see a new kind of enemy implemented using the same topic of Models used for this game. Unless Frames were used again, I don't want to see Miis. It's not that I don't like them, but they really don't give an enemy-related feel. They're meant to be cute, for the most part, and that doesn't bode well for evil. Unless you're B.B. Hood are other various characters, it just doesn't work too well. But that's my opinion, of course.
