What do y'all think about mailing lists and IRC as sole communication channels?

These technologies, although archaic, clumsy and insecure, are not a fatal problem - these are still open and widely accessible anyway.

However, this case may indicate that the projects author is an autocratic hermit type, locked in a bubble with his ancient tech and not really welcoming outside contributors and bug reports, so these IRC and maillists come with worse things such as CVS, C89 code, build system handwritten in shell which only works on author's machine, and complete unwillingness to discuss, fix, modernize and make the software more portable, so not only contribution attempt would be a waste of time, but simply using such project could pose risks.

Of course that's not necessarily the case and it may be just good old IRC and maillists, and that should not be the problem for most people. For me personally though, for I contribute to hundreds of F/OSS projects, this is a show stopper, as I absolutely want to minimize routine tasks. One-two git/gh commands is what I'm used to, while installing extra software, going through registrations, copypasting patches, monitoring additional sites for feedback does not work. In the best case I would fire-and-forget, so if someone on some god forgotten self-hosted gitlab asks to fix a thing in my PR I will never see it. Or more likely, I would put such contributions into my contribution queue with lowest priority, and since the queue of what I want to improve is always growing and never shrinking, it effectively cancels them.

And I could add that you don't really need realtime communication channels to contribute - technical stuff may and should be discussed in async mode as in issue/PR comments (or email reply thread in the worst case), where unrelated discussions don't happen in parallel, message size is not limited, history is preserved, nobody is in rush to reply, you don't need to actively wait for reply and cannot miss it because you've disconnected, someone forgot to tag you or it was just list in the chat.

Summarizing, the project should be on [the most popular VCS hosting at the moment], which is currently GitHub, any other choice makes it much less accessible and welcoming. For chat use whatever you want, for it's not related to contributions. If you think otherwise, at least stick to open protocols.