His style doesnt suit a heel role
I agree. It would be the equivalent of having Junkyard Dog, Koko B. Ware, Dusty Rhodes,etc. turn heel. Just will NOT work. There's just certain types of crowd favorites that will always have to remain that way.
You see i disagree. If you can make Hogan Heel then anyone can with the correct writing.
If he came out and crippled HBK with a chair.... then came out and beat up a women and then insult the fans and then preach like CM Punk does.... he'd be a heel. And to top it all if he started on about Eddie... He'd be booed. Which in essence is a heel.
He may have to chage his in-ring style to include less flashy moves.
Whether WWE and Rey want to put that much work into making him a heel is the question and to my mind they need him as their only credible Latino star. Plus you'd have to go OTT in making him a heel and that would probally be irreversable.