Regarding:
“(a) My impression from some semi-recent discussions here and on the Mastodon Discord is that there's much more momentum for abolishing host-meta support than for abolishing WebFinger.”
One (I think) useful thing that people use host-meta for is — to specify that WebFinger is on another host.
If host-meta is abolished, do you know if they have a plan to replace that functionality using some other mechanism?
(Maybe a DNS TXT or DNS SRV record?)