[Keith]

Which is why it makes even more sense for the new channel to move into D in April, if it's going to be many months before E can be fully refurbished and is ready.
C can be kept going on a back-up/standby basis and for the Breakfast & weekend BBC London updates that just need a fixed camera and backdrop.

I could be wrong but I believe reading that the cameras in D aren't on tracks, so presumably any repositioning of them would have to be done manually. Whilst fine for regional news bulletins it's not ideal of a rolling news channel, where you may have guests coming in and out of the studio throughout the day.

Baring in mind the BBC appear to be going for a soft relaunch I'd imagine they'll continue using C whilst refitting out E, or possibly vice-versa. That way any change is less noticeable at first glance to the viewer, as the set in the studio appears to be the same (or at least familiar). There's also more space for guests/reporters to appear in the studio alongside the presenter.