Make it look nice and be simpler/easier to use. Support more hardware. Advertise it more.

Unfortunately people like what's familiar... and so to really appeal to the masses you have to inch further and further away from what actually makes plan9 different from everything else, at least visually.

I have a thinkpad x1 nano, not sure if that is considered old or not.

I've ran: Windows, Debian, FreeBSD, and OpenBSD on it and OpenBSD is the one I've gone back to and kept because everything works out of the box (except maybe the fingerprint reader - not sure because I don't use it anyway)