The North London Line / West London Line will be getting six 5 car 710s for service uplift, and so some 378s can be cascaded to the ELL for service uplift there too. It seems likely they will cover the Richmond-Stratford service given they are fitting TPWS on the Richmond branch. I haven't figured out whether the 710s will cover all the Richmond-Stratford diagrams or just some of them (though visually distinct trains would certainly make it nice and easy for the passengers!).
Surely not *all* services? There has to be more than just 6 trains on that service.
However, it might be that they will be dedicated to that service, that is until service disruption sees a 710 end up going to Clapham Jcn via Olympia!
You're right of course, I suppose given a diagram seems to be just over 2 hours, maintaining a 4tph service would need at least 8-10 trains rather than 6.
I suppose the idea must be that all Overground trains will use the TPWS overlay/underlay to CBTC on the Richmond branch once that's all complete. The tripcocks on the 378s will become redundant as the trainstops are removed when this happens. Both the 378s and the 710s should be able to go anywhere on the NLL/WLL if that's the case.