That suggestion doesn't even make sense. That person dead *** combined one of the Annihilation events (I think it was called Conquest with Ultron) and added in Hulk for w/e reason.
But it's Adam Warlock, right? I'm only guessing that because he already said no to Nova and I can't think of any other legit supporting characters for the GOTG
It could be a Space Knight that looks a lot like Rom but is different to avoid being sued (surprisingly tons of ppl that were in to comics at that time period love Rom).
Maxam maybe (black guy from the future trying to change the past - a Badoon invasion I think - using an infinity gem that was in the Infinity Watch book. Believe it or not I don't think he was a Cable and Bishop knock off, may be wrong though )
Wraith - some Kree dude with an alien suit
Gunn knows he's probably like the only guy helming a franchise where he can keep fans on their toes. The Guardians haven't had huge classic runs in the comics, don't have many memorable stories so you can be guessing forever for a subtitle especially when he straight up shoots down the most recent memorable ones.