I'm a big fan of the IndieWeb community, yet I've long struggled with using many of their protocols or guidelines. POSSE is one of those. I do POSSE content to a couple of platforms (though, so far, I haven't made the original "source" posts on this site public) but I do so manually, and I likely post more on those platforms natively than I engage with this system. That isn't due to any specific friction or issue, but more because I'm happier having my content distributed across multiple places. That said, since moving to Mastodon I have been toying with a "stream" domain – we'll see if I ever actually make it, though!
On the rare logic of why automation is not the answer:
I've decided I'm going to discontinue using automation in favor of manually writing posts for each of the platforms I want to post to. [...] I'd like to syndicate to more platforms and each of those have their own look, feel, and community driven norms.
On the loss of native functionality (this is something I've been thinking about a lot, and one of the key reasons I don't think I'd ever want to clone a note to multiple note platforms, e.g. Mastodon and Twitter):
Micro.blog does not support hashtags whereas on Mastodon and Twitter they are first class citizens. By POSSE-ing via this method I lose out on all of that.