Accomodate cross-platform mentions (to GitHub users)

Not sure whether random ideas like this get posted, but wanted to jot it down real quick. If it belongs elsewhere, then just point the way, and I'll park it there. (Won't be a project I'd have time for, but would like to share in case someone else more active on GitLab has energies :) )

I don't use GitLab because some of the communities I'm most interested in working with (eg. civil servants just getting used to GitHub) are not on GitLab. But if I could easily @mention them from GitLab, that would make it a little more enticing.

GitHub Apps don't allow custom notifications, but perhaps github issue notifications could be hijacked by a bot app.

If a bot on GitLab looked for a certain mention format, for example <github username>@github-bot, then the bot would know whenever it was mentioned. It could then lookup the github user, and in a special repo on github, open a new ticket, @mention user there, and post a link.

I feel that this could help stitch together these fragmented communities. It could also go both ways.

Thoughts? Any thoughts on where I could park this concept or share it in a better venue?

Thanks so much, both for your time here, and for those doing work on GitLab itself <3