That was intriguing, my first thought with the Coulson at the end is an that he's from an alternate universe.
I don't know, they've essentially already done the alternate universe/timeline Coulson thing with the framework, and it's not like this show has much of a history of recycling ideas. Of course they've already done the impostor thing and the amnesia thing too, so not sure what else is left?
With AoS's "unique" history in handling it's regular characters, my guess is that Phil Coulson is gone. I mean dead, really dead. And this new doppelganger is who we'll get for season 6 and maybe through the series end. We got no rollback of Grant Ward, and I don't think we'll get one for Coulson -- unfortunately.
Maybe it's just a someone who looks like Coulson for some reason, but has no actual connection to him.
Did we ever find out for sure if the Koenigs were normal identical siblings and nothing more than that?
I'm pretty sure we've never gotten anything definitive behind the Koenigs but it's suggested (by them, I believe) that they're just siblings. Also, they really need to return already! I've loved the sheer madness of the last couple of seasons with our team all over the place and time, but it's time to bring back the Koenigs!
Mac tells May that he's glad that she and Coulson got to spend some time together before the end. May replies "We got more than we thought we would." On the surface it seems like a innocent enough statement, but what if there's a deeper meaning? Suppose something happened at Tahiti that May is not talking about. Something that may perhaps have something to do with this duplicate and/or amnesiac Coulson that we saw in the trailer.
Spoiler: Clark Gregg's new character Hmmm, so he is not Phil Coulson, it will be interesting to see how literal that is or how much wiggle room there is in that statement. I have learned not to take statements like that at face value when it comes to this kind of stuff.
My money is on amnesiac Skrull, because if you're gonna speculate wildly, may as well swing for the fences! Also, it'd be a way to kinda/sorta tie-in with Captain Marvel. Like, this guy copied Coulson back in the 90's and for whatever reason, has been stuck in that shape ever since. And I tend to agree they're probably going to let Coulson stay dead this time. It would kinda cheapen that final send-off if he manages to shrug off death a second time.