Unlikely they'll get a full repaint with GBR on the Horizon. With Gat Ex 387s running around on the coast.. and on Bognor/Eastbourne to London Bridge peak services, it's a bit of a mess.I should also add that there are differences in the interior, namely that the Class 377 has good old fashioned comfortable seats and the Class 387s have ironing boards. Nearly all of the seating throughout the train is 2+2 as well, rather than the mix of 2+2 and 2+3 present on most Class 377s.
In general, the inability to operate Class 377s and Class 387s together I would say is it a bit of bummer. However, if they are predominately allocated to either the West or East Coastway generally in the long term, its not much of an issue, given the trains usually operate as single and uncoupled 4-car units, and I suppose if they ever needed to extend them to 5-cars should demand ever increase (which I highly doubt given fares will probably end up skyrocketing at this rate after this so called "trial" on LNER, which there is another thread all about), then they could do that with some units which are semi-permanently assigned to Southern. Although most platforms can handle coupled 8-car units, in most cases its of little importance to regional services in most cases.
I suppose one of the future refreshes they could do with those units will probably be eventually to repaint them into Southern colours, so they more closely match the Class 377s which they are partially displacing, presumably to allow a few to head off to Southeastern, whilst still boosting capacity (presumably) on London suburban routes, given Class 377/3s could be soon be made largely redundant except on Bognor Shuttle and Seaford services (where you can't really justify 4-car trains to the same extent as other routes.
I believe most 387s will run services on the coast. What they replace and where those units go is up for debate (apart from the 13 going to SouthEastern).
Personally... I like to see the return of peak Cat and Tatt to Vic services.. and more longer metro trains on Saturdays.