I had a similar question. And I'm still not clear from the response
what exactly index_blks_total is and whether it addresses it.
I think I agree that a user is likely to want to see the progress in a
way they can understand which means for a single index at a time.
I think what you're describing is that index_blks_total and
index_blks_scanned are the totals across all the indexes? That isn't
clear from the definitions but if that's what you intend then I think
that would work.
(For what it's worth what I was imagining was having a pair of
counters for blocks scanned and max blocks in this index and a second
counter for number of indexes processed and max number of indexes. But
I don't think that's necessarily any better than what you have)