Recently Jeff stated in an interview that he wouldn't mind working as a heel before his career is all said in done. It wouldn't be the first time as he used to be a heel in his OMEGA days, but has yet to do it since gaining his cult-like following with the WWE.
But would it work or would it become a total flop? Look at the big time baby faces who've attempted to turn only to fail miserably. Goldberg. That lasted a week. When TNA recently tried to turn Sting, he ended up cutting one of the best promos of his career. Instead of getting beer thrown at him he was doused in cheers.
To become the best of the best you've got to be able to work both sides. Jericho, Flair, Triple H, Angle and even Hogan are able to work the crowd either way. And for this they will go down as some of the best that ever stepped into the ring.
It's really hard to be taken seriously as heel if 13 year old girls are throwing themselves at you. Well that is unless your name is Ric Flair. But he's the exception not the rule. The only way for Jeff to draw immediate heat is to turn on his brother Matt (and even then he might get applauded). If he were to cost his brother the ECW belt this would ignite a jealous feud that would be on par or better with Hart Bros feud.
In the end I don't really see it being done. I don't think Vince would pull that trigger. I do believe the Hardys will go at it, but it will be more like a healthy competitive one-upped ya kind of thing. If Jeff is able to make me want to spit on him as he walks to the ring, it would be an amazing turn around.
Or maybe all he'd have to do is act like he could care less about the fans, so what if he's failed multiple wellness checks, and he does what he wants to do. That could get on some people's last nerves real quick.