It has been proposed a few times I guess, and while Lemmy.ml seems to be not actively hostile against “us”, I would say it is very much in line with the anarchist idea to decentralize and become self-sufficient.

However so far no one seems to have stepped up to actually run such an instance, or am I overlooking something?

I personally have thought about it (I have a quirky 3 letter domain name that I would find fitting and also run my own servers), but to be honest I am not deeply embedded in the anarchist community (more of an anacho-individualist in that sense, despite being in favor of syndicalism in theory) and probably also have some other unpopular opinions in some ways. I am also a somewhat grumpy old white male not very keen on moderating community drama.

tl;dr: I think it would be cool to have something like that, but I fear that me starting (and mostly running) it would soon not be very popular and I am also hesitant having to deal with the likely hassle of running something like that.