Shouldn't be that difficult to down- or upgrade to the required version (via a patch or mod), If it's just slightly different?

There is no way to do that. Some smaller mods are already incompatible because the modders just don't bother to make a GOG Skyrim compatible version.

The only hope in this case is that GOG will update Skyrim accordingly to work with Skyblivion. But I don't know how likely that is.

That's cute! While you kids play around in a toy version of Nirn that had all the edges smoothed off (and missing several schools of magic), here's a project to put all of Tamriel into Morrowind that doesn't care what version of the game you have*.

*I doubt it'd work on the Xbox version, though.

Well, this one will wait for Skywind. I do own Morrowind here on GOG, have it ready to play and everything, but it didn't quite grab me yet. Maybe I'll give it another go waiting for Skyblivion?

Also, update: maybe a false alarm on not supporting GOG? I'm now being told they want to try have the GOG version supported. Still, doesn't change my original point - the version difference between GOG and Steam versions is causing issues for modders and people who want to use mods.

That sounds like necromancy talk...

I'm reporting this to the Mage's Guild.

You and what army? I killed their dunce of a leader and didn't even assume the role!