There was, and remains, a lot of pushback from BA FFs about Max's being added to the fleet. It was actually taken onboard by, then, management but of course it's anybody's guess what they eventually do regarding that pushback.
The comments about at least some of them being placed at LGW for the new EuroFlyer brand so it has seat density to compete with EZY and TUI is logical and although no blog I've read about this has yet picked up on it. Boeing did build a maintenance hanger and facilities there only a couple years back which would add a reason for placement there but at the same time none of the crew based there has flown on a Boeing single aisle in longer than I can remember so 8t would require both pilots and CC to undergo total retraining. Whilst that actually applies across IAG as a whole the unit costs of that training are substantially higher in the UK than in other brands locations and we aren't talking small change in that difference either.
Vueling is the 'natural' choice simply by pax demographic and ULCC model so I think we might see some reallocation of 320 fleet across brands feeding them to EF in a swap out / cascade approach. They already fly into LGW so could avoid the need to run empty ferry flights for maintenance. IB express being another contender