We've already found a few bugs in Postgres and upstreamed fixes for them. There is a patch or two from us in their review pipeline right now.

Yes. Some of them, like strict parsing of timezone-aware vs naïve datetimes can be upstreamed (as a configurable option) if the Postgres community accepts it. It's in our interest to upstream things like that :) We'll see how it goes.

May I assume that the slight modifications you were required to make to postgres in order to support your features weren't just bug-fixes?

An occasional post tracking the status of that upstreaming effort would be very welcome.