There's a LOT of infrastructure that already exists in the Hack ecosystem at Meta. Especially around things like data access control, privacy, auditing, data deletion, etc.

When I left earlier this year, pretty much all of the internal storage systems (from MySQL to blob storage) were moving to requiring all access to be via a common Entity framework that encoded the above-mentioned things in a common way. That framework exists on the non-Hack side of the house, but it's much, much easier and in some ways more robust on the Hack side.