This very thing came up in a conversation with PeterG early last year. I was in favor then and I was surprised that the only thing standing in the way was a lack of ALTER TABLE syntax.
Creating temporary data structures to mimic existing metadata structures is a pain.
It'd be even better to also add a REINDEX flag to COPY, where it disables indexes and re-creates them after it finishes. But that could be done separately.
I'm iffy on the COPY change. If we add index rebuilding, why not disabling as well? If the COPY fails, what state do we leave the indexes in?
I'm not sure I can tackle this in the current dev cycle,
I may have some spare cycles to devote to this, but it's unfamiliar territory. I'm happy to do the grunt work if I had some higher level guidance.