[Worzel]

I suspect it isn't helped by the fact that the backdrop screen in studio C is a) now over 10 years old and has been in pretty continuous use since 2013 and b) is probably not 4K due to its age. Technology and screen panelling has moved on considerably in 11 years, as has the reduced cost of producing them. For example, 4K consumer televisions are pretty much standard and the norm when you buy them from retailers now. Most domestic retailers were flogging 1080p HD televisions in 2012/2013.

When the news channel used the updated rendered newsroom backdrop on the plasma screens in D it always looked much better.

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.

Studio B's refit must surely have be easier because of its location in NBH and being a proper television studio and out of the way of the newsroom.