Normal for airlines to be adjusting aircraft types this far out as they balance expected demand and route networks... we've only just started the summer schedule so don't put much weight on the winter schedule types right now.

Happen to me in the other direction a couple of years ago. Booked BA5 in the winter schedule as 777 and a month later (probably about April TBH!) it switched to a 787-8 which was a bit of a downgrade! A350 on the return home was really lush though.