I was wondering the same thing. But at the same time, it seems like having it all centralized in one place would make it really easy to write tooling to aid in

I was wondering the same thing. But at the same time, it seems like having it all centralized in one place would make it really easy to write tooling to aid in such an endeavor. For example, suppose it was decided that sharding would be by account ID. It would probably be very achievable to have some monitoring for all newly created relationships to check that they have an account ID specified, and break that down by relationship type (and therefor attributable to a team). Dashboards and metrics would be trivial to create and track progress, which would be essential for any large scale engineering effort.