Should CM Punk come back as heel? Certainly, I don’t see why not. Punk has managed to stay over with the crowd despite the numerous amount of burials he’s received from the Big Show a while back. That alone proves that he is one of the most over heels in the company to this day. But now, if you have the guy come back as a tweener, he can be a face and still go out on his way and do heelish ways such as with his straight-edge gimmick (etc.)
As for the second question of this thread, that’s a rather complicated answer. Technically speaking most of the heels in the WWE are already tweeners. By definition, a heel is a person that is supposed to be hated by as many as people possible; yet, nowadays, that is rarely the case. When was the last time you saw the majority of the people hate someone like Chris Jericho (arguably one of the top heels of the company)? Fact is, not many hate him; mostly everyone likes him; more importantly, mostly everyone cheer for him. Now, if Jericho is being liked, then technically speaking, he is not a heel; he would classify more as a tweener than an actual heel. Heels are supposed to be hated; yet Jericho isn’t…do you see the connection here?
A true heel is someone like Michael Cole. The guy is hated on by ALMOST, if not everyone. The guy cannot go 10 words without being boo’d by the crowd. I see people complaining, bitching, whine-ing about how Cole is an annoying fuck all the time. But the interesting thing here, is that Cole is merely doing his job---getting you to hate him.
Of course, just because one is a heel does not mean that you can’t like him (or her), it just means that technically speaking, it makes them more of a tweener than an actual heel. But as I said, the clarification in determining what a wrestler actually is relies on the technicalities of said situation. However, most of this technicalities is revolved around how the fan interprets said wrestler. If you like a wrestler that is a heel, the best way to support him is to ”Boo” him; if you like a face, the best thing you can do is cheer for him.
Alas, this rarely is the case for the average viewer and they just cheer for the wrestler regardless of the situation. But hey, what can you do, right?