Tom King got permission to do something really big to change the character in the last 15 issues of his run (which I guess would start next January and go through summer). Supposedly it's long-term and permanent, but if he's doing this before he ends his run, what could be so big to force new writers to go along with it? At least for quite a while.

Any theories?

Most popular guesses seem to be 1) Publicly unmasking him, 2) marriage for real this time, 3) Killing someone, 4) Retiring/quitting

I think retiring has been done several times in the last decade, so that's unlikely. I think him and Selina will get married, but I honestly don't know if that qualifies as that big of a change (it is a big change, but you'd think the next writer could certainly get rid of that quickly if they wanted).

The public unmasking is a big deal. That would definitely have long-term repercussions. I think that's possible.

I really don't think he'll kill anyone, but I guess that would definitely be changing the character. I just feel like that's doubtful for some reason.

Another possibility I've only seen a couple of people bring up is a baby being born. He's had tons of kids obviously, but a baby would be an addition that's hard for new people to get rid of, as we've seen with Damian. So that could happen too, imo.