I think that Gray hulk is also A hard incarnation to get exactly right. Every time he is shown previously he's always been depicted as "Joe Fixit" when that was always an alias that he used, nothing more. Portraying the character as only a thug limits the storytelling potential, at least in my opinion. It's the same problem as always betraying the Savage Hulk as "Hulk smash" and little else.
I think the time for the grey hulk be the dominant personality has passed. I'm not against his return at all, maybe for like an arc or two, but I don't know if he could work on a full-time basis, like he did when PAD was writing him.
But who knows, maybe if they got a really good writer to reinvigorate the gray Hulk and take them on new adventures instead of just always having him fight in Las Vegas, it could be really interesting.
You never know.. given Marvels tendency as of late to look backwards instead of forward i wouldn't put it past them to try and hire PAD to bring him back.
Especially since he needs the money and is currently writing a book set in Vegas currently.