I don't think he would make a good Cena type babyface, but maybe a very successful Punk/Jericho babyface. Who is still technically a face, but is not clean, nice either. More like classic Jericho. I think Dolph could fit that tweener role very well. The crowd at this last Raw was totally backing Ziggler. After he pinned Swagger they erupted. The even chanted "Lets Go Ziggler" through the match.
Ziggler is the perfect example of a slowburn push done right. They didn't sky rocket him to the top, but they slowly let you see his greatness and they worked him to the top. I think WWE handled Zigglers career very well.