Great to see these sorts of things, Postgres has been amazing and glad people realise it.
I assume for the common Postgres core changes everyone is already incentivised to contribute changes back upstream - the companies are banking on Postgres popularity can need it to have an excellent reputation even outside of their specific customised offering.
TimescaleDB and Citus are notable too.
But yeah, if you’re building a DB product, starting with Postgres and customizing from there seems like an excellent approach.
What would be an ideal resume for someone who never worked on Postgres