[Radio_man]

Ok, so if the backdrop in C cannot be improved, the BBC's new flagship news channel should at least be 'soft launching' from a decent studio, for example from D, that has at least been refreshed in the new BBC News studio look.
Then move all BBC 1 network bulletins, Hardtalk and the main BBC London bulletins into B, and keep studio C for BBC London at Breakfast & weekends, and possibly for the first few months as the UK only 'breaking news' studio.
Newsnight can still come from D as it looks like the News Channel would be finished with D by 9:55pm every weeknight.

I suspect the refit of studio E is actually going to be quite complicated because of where its situated right in the middle of the newsroom and will likely cause some disruption to the journalists situated on that floor. 

My guess is the staff based at the desks will have to move to allow the studio to be refitted with set riggers/builders being there and all the extra noise.

I would guess they'll use the opportunity to upgrade the cameras in E to the same ones recently installed in B and carry out the necessary gallery upgrades at the same time.

Finally, I assume they'd also replace (or completely remove) the broken newsroom hoop on the roof and replace the blown strip lightbulbs and spotlights in one go.

When you think about it and break it down, there's quite a bit they have to consider in preparation even before they start any studio refit.

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.