They’ve also clarified a few things. From Marcin Momot:
The GOTY version of the game will be the base, both expansions, and all 16 free DLCs that they did. Plus there will be a standard patch updating/fixing some issues for all versions that anyone gets.
If you have the base on PC, you can buy the GOTY and you’re fine. But–they recommend you just get the season pass, because that’s cheaper. You’ll have all the GOTY content.
If you’re on console and just have the base game, also buy the season pass. Again, it’s cheaper, and you’ll get all the same stuff as in the GOTY version.
If you’re on console and have the base game and buy the GOTY version alongside it, the console environment won’t allow you to use your saves. Why you would do this is weird in the first place, but whatever. You should know though that consoles think of these as two separate titles and won’t let them cross-pollinate saves.
And…this isn’t anything new. I bought Arkham Asylum on release day way back when, and didn’t get around to playing it very much and figured I’d never play it all the way and sold it back. Then when Arkham City was coming, I wanted to play AA, so I went and got the Arkham Asylum GOTY version for 360. And the saves from my release day version didn’t work with the GOTY version.