I'd love to see a gathering of the annoying B-island survivors. Arzt, Frogurt, Nikki, and Paolo, etc. I think that would be funny as hell.
Still not sure why Michael is trapped on the island. He did a terrible thing no doubt about it but he did come back to help those left behind. Kate, Sawyer, Sayid, and Ben have done terrible things before and after they left the island.
Besides the actor not wanting to do the show, Mr Eko is nowhere to be found either and he was studying to be a priest.
However, I'm wondering if it was because Micheal was tricked by the Others who are supposed to represent Jacob into doing what he did is the reason. Not sure.
I think it had more to do with the fact that Michael was someone Jack simply could not save. Further, Michael was someone who betrayed all of the castaways, even if he did redeem himself later, it wasn't directly with Jack.
The blink-and-you'll-miss thing about the finale is that up until the church scene, the flash-sideways all season long I think have been about all the characters reconciling their deaths. The church scene however was only for Jack, and so only the people who were important to him during this "most important time in his/their lives" (i.e. the island) were there: Christian, Kate, Sawyer, Juliet, Hurley, Jin, Sun, Locke, Shannon, Boone, Libby, Sayid, Rose, Bernard, Desmond, Penny, Claire, Charlie, Aaron ...etc.
This is not to say that they each didn't also have their own version of the church scene where the people most important to them were present; it's just that
this particular scene was for Jack's sake.
It also says something about Ben's character that even in death and what was likely a long life after Jack's death in which he could have redeemed himself, he still chose not to go in to Jack's church scene.