Hello .Yes! that would be awesome!
I signed my FSF agreement some time ago but it should still be valid.
Agreed, there's not an expiration date on assignment AFAIK :D
Even though this is a fork, I've coded the majority of it (we started it with a friend under his user, but I took the ownership of the repo since very early).
A quick look though the substantial number of commits to your version suggested the same to me- it looks like most of the code is new or rewritten in your version.
Do we have to measure contributions from other people and reach out? or, if I rewrite their code, is it ok? because IIRC there's been just a handful of contributions from others.
In an ideal world I would suggest reaching to each contrib; if everyone has or would be willing to complete the assignment process it may simplify things.
Alternately (or if there are some we can't reach or who can't complete the assignment process), I think we would usually essentially count lines of code related to (non-trival) change. IIUC, contributers having 15 or fewer LoC in the project need not assign copyright. That said, that LoC limit is a lifetime total, meaning if a given contrib had 10 LoC in erc-image but already had submitted 10 LoC to something else in Emacs (and had not completed assignment paperwork) that would put them over the limit and we would need their assignment to proceed.
If this get's complicated a first step could be adding this into the new Non-GNU ELPA repository. We can add some folks to the thread to discuss that if/when that seems like something to dig into (assuming it sounds good to you). Non-GNU ELPA has the advantage of being available as a default package repository starting with Emacs 28 (now in pre-release testing).
Aside: I'm developing a patch for you to consider which is what lead me to reach out. I'll make a new issue on GH to discuss that. (FTR, I do have assignment completed ;)
Thanks again for your response and for erc-image; looking forward to seeing this great feature get wider reach.
Corwin