Optimize INSERT performance with a UNIQUE constraint on md5(JSONB_COLUMN::text)
If the uniqueness constraint is the only issue (and I'm interested to learn more about why in the discussion above), here's an idea: 


remove the uniqueness constraint
when you do reads (selects), do order by id asc limit 1 so that you ignore duplicates
have some sort of parallel process going through the table periodically and removing duplicates