Also are you 100% sure Company doesn't do this? I'm pretty sure
it does this when there is only one completion, at least.
No, I'm sure Company does do more or less this. As you say, and as I
mentioned upthread, Company provides a preview frontend that kicks in
when there's just one completion candidate by default. (This is in
contrast with `corfu`, that provides no such preview.) There are some
differences between my implementation and what you get with Company's
preview frontend, but if Company would make it to core Emacs that would
indeed mostly obviate the need for my `completion-preview`, at least as
far as I'm concerned. Is there a viable path for upstreaming Company?
I've suggested this in the past, and it's mostly for Dmitry to answer,
but IMO that path should definitely contain a scaling back of Company's
company-backends infrastructure, basically importing only company-capf,
which is (IME of course) the only real backend we should focus on. This
would help sanitize some of the incorrect perceptions of complexity in
Company setup (the kind that Alex's argument suffers from).