Differential seat availability (as in physical seats on the aircraft) is a feature that is available in FLY. The result is that the seat map is not necessarily the same for everyone. This experience suggests that BA is using (or at least experimenting with) this exact function. This may also be the underlying reason why "public" (GDS) displays (eg via EF) are showing so many seats as blocked - so that FLY can do its work without interference from TAs and other public portals.

I think that soft seat blocking (eg next to higher-tier members) is also something that FLY can do.

Where BA will go with all of this in the long term must be a matter of speculation.