You appear to be saying that you think that renaming an index concurrently is not safe. In that case, this patch should be rejected. However, I don't think it necessarily is unsafe. What we need is some reasoning about the impact, not a bunch of different options that we don't understand.
I've had this same need, and dreamed this same solution before. I also thought about a syntax like ALTER INDEX foo RENAME TO WHATEVER-IT-WOULD-HAVE-BEEN-NAMED-BY-DEFAULT to aid this situation.
But all of those needs fade if we have REINDEX CONCURRENTLY. I think that's where we should focus our efforts.
A possible side effort into something like a VACUUM FULL CONCURRENTLY, which would essentially do what pg_repack does, but keeping the same oid and the stats that go with it, but even that's a nice-to-have add-on to REINDEX CONCURRENTLY.
