Well, Tim Hunter has always been in the mainstream universe. It’s just that he has mostly appeared in comic titles published by DC’s darker imprints like Vertigo and Black Label, with few exceptions, like his brief tenure with Justice League Dark during the New 52 era. Will he appear anytime soon? Maybe, maybe not. Considering he starred in a title that only just ended last year, DC may not be ready to put out another title for him soon. Who knows, he could make an appearance in a DC-proper comic, but that’s not usually where he’s used.