In bug 1289536 we are landing event telemetry in the sync ping. However, the client APIs aren't yet capable of recording events for pings other than the main ping, so the sync code duplicates the logic for validating, storing and submitting these events. Georg tells me the intention is for the client APIs to be capable of doing this and thus making it possible to remove this complexity from the code managing the sync ping.

This is planned, but we are not at that development stage yet.

I think this will be covered by bug 1302681, but it could be helpful to keep track of this requirement in a separate bug.