Hello,
As far as I am concerned, I am totally awaiting for this kind of feature exposed here, for one single reason at this time : the extension pg_statement_rollback will be much more valuable with the ability of processing "rollback to savepoint" without the need for explicit instruction from client side (and this patch is giving this option).
The way the improvement is suggested here seems to be clever enough to allow many interesting behaviours from differents kinds of extensions.
Thank you,