With Bryan's future looking bleak, the WWE is in dire need of grooming a babyface that the entire audience can relate to and cheer for.
In the mold of Steamboat, Guerrero, Bryan, and possibly Foley, Zayn is a top-notch worker who the fans can't help but love. As he has proven down in NXT, he's just able to connect with the audience like few other workers can. Bryan has shown that, more than anything, that is what the fans want the most. There is a reason why, despite Punk having the "cool" factor, Bryan was obliterating him (and everyone else on the roster quite frankly) in crowd reaction prior to Punk's retirement.
Zayn isn't as good as Bryan in the ring, although he certainly isn't lacking in that regard. I love Zayn's moveset and his ability to sell his opponents offense. Zayn is a better mic worker than Bryan, in my opinion anyway. Bryan isn't bad, but I just prefer Zayn who I think has really become strong in that area. Zayn is the most over singles wrestler on NXT and IMO, once he is moved up to the main roster, he could be the guy that really fills Bryan's role if Bryan unfortunately has to call it quits.