Enthusiastic enthusiasts making predictions? Here? Neeeeeever!
Well given that
@OmniCity999 is very much in the know and has a track record of being proven so, I recall a previous comment where he mentioned they like to keep types together wherever possible, so my gut says the 7900Hs would stay in the city fleet, especially as they've just been through refurb / repaint.
I also remember another comment where under the end result of Bus2020 all singles would be Euro 6.
So my guess would be City fleet could end up as just 7900H and B8RLE, with the 79s freed by the new arrivals being cascaded round City routes to oust the B7RLEs.
The newest E5 surplus B7RLE then go to LCB/ECB to replace the older B7RLEs (ex Arriva and the 04s surviving there) with the next newest renewing the training fleet and the rest going for disposal.
The retained B7RLEs can be E6'd as per the 13 plates that moved to LCB already.
At least, that's what I think the thinking would be pre COVID. Wouldn't be shocked if that's thrown a giant disease ridden spanner in the works.
/End rampant speculation based on loose maths and crystal ball powers developed during lockdown!