Any plans on updating this mod for the experimental version?

I haven't had much time for Factorio lately. There are a few bugs in a few of my mods that I had hoped to fix as part of a 2.1 update. I'm open to pull requests, but might not get to them in time.

No worries, hope life is working out for you! Take your time.

If I wanted to make it updated for 2.1 myself, does it need anything special? I doubt there's anything that would break this mod going into 2.1 yeah?

There are two competing PRs for 2.1 compatibility already. Testing and improving one of them would be an excellent way to make progress.
https://github.com/sparr/factorio-mod-automatic-underground-pipe-connectors/pulls

When attempting to upgrade to 1.2, I got the following error.
LuaEntity doesn't contain key fluidbox.
stack traceback:
[C]: in function 'index'
__automatic-underground-pipe-connectors/control.lua:217: in function <automatic-underground-pipe-connectors/control.lua:68>
Edit: Looks like this was covered in Issues in Github.

,

for the time being (until sparr finds the time to release the changes himself) I created a release of the 2.1 version here:
https://mods.factorio.com/mod/automatic-underground-pipe-connectors21

This version will be deleted as soon as sparr is releasing for 2.1 ofc! :-)

+1