It's possible, but unlikely, that they could pull a City Slickers 2 and have Gregg play Coulson's identical twin. Or that Coulson will be a virtual reality or holographic character based on the original.
But it does look like the real thing is back. Brilliant news. Kinduva cheat but I do think that the clues are there in the original movie that he's not really dead, so it's not a total cop-out, IMHO.