Somehow I’m not that concerned. I haven’t heard of any company but Nintendo trying to assert rights to 1980s game IP, and that’s because they’re still selling those literal ROMs as part of a subscription service.

Would I port such a game and then sell it? No, because that kind of puts a target on your back. Keeping it open source and also noncommercial, I don’t think it’s ever gonna matter.

(Obligatory I’m not a lawyer disclaimer - this is a vibes based comment not legal advice. Obviously copyright is nearly infinite, in theory)