Well, I've slept on it, had a think , and read the posts.
A lot seem to have asked why Mark wasn't there?
Given the likely speculation over the title , the fact he has "disappeared" at the end of TLJ in such mysterious circumstances and then there was the Palpatine reveal ,it would certainly make sense to leave any hint that he's still around until much nearer the release date.
Now the focus is on Palpatine and everybody is trying to guess which Skywalker is going to rise, which is clever. But I'm guessing from the voice over Lukes a force ghost, I really cannot see him being anything else.
He says "We've passed on all we know. A thousand generations live in you now. But this is your fight" and then adds "We'll always be with you. No one's ever really gone." which says, at least to me, there is no chance of him being anything else really "substantial" in the film for any length of time, but given the dice trick in TLJ who can tell.
I'm ok with the Palpatine angle. The fact the "First Order" appeared as literally another Empire after its downfall seems to hint that Palpatine left a " first order" (like Order 66) which was an instruction that in the eventuality of his death it was to be recreated. I always thought that after TFA we'd see Palpatine emerge as the power behind Snoke ,Wizard of Oz like.
Afterall there has been no real explanation how Palpatine became the Sith in the Prequels so thats very open. But I highly doubt that he cheated death at the end of ROTJ as a living body (he fell down a shaft, blew up, then the whole bloody DS exploded !!!!!!), but perhaps did remain some sort of dark influence that survived it, again likely as a force ghost. Remember its only much later that Obi wan and Yoda discover this ability to "survive" death as Jedi.
Or maybe he's even something else entirely, as part of a greatter evil always within the Force. The Sith does seem to be a pretty persistent entity as a reemerging corruption of the Jedi values, so maybe reincarnating itself into a living physical body to take action in the universe is one Sith spirit in particular (hint, hint !!).
I did sketch out several story plots after TLJ to see if I could get the story back into line and that was my thinking and the trailer and panel kind of hints at this.If they manage to wrap up the entire three trilogies in even a reasonable way that allows the entire SW universe to move on I 'd be very happy.