The donation of ECS to OpenTelemetry will greatly help, and most of the new schema development will happen through contribution to OTel Semantic Conventions. There's an open ECS PR documenting this expectation, if you have any feedback on how we document this for the ECS project.
For example, a strawman RFC was submitted for RPC , but has not moved in three years.
RFCs rely on contributors to advance their proposals. If the original author(s) don't move the proposal forward or other interested contributors continue the work, it's possible for a proposal to stall.
RFCs can be marked as Stage X if a proposal isn't moving forward in the near term (but still could advance in the future), so IMO the RPC should be updated to Stage X.