Litebulbs - BA cc legal limits are the BA scheme, which is based on CAP 371, and approved by the CAA. There are often subtle differences.
Even with those CAP 371 limits, it is legally possible to operate 2 b2b trips, as most longhaul trips are 3 days. Longer trips will usually have 2 local nights off downroute, so even they comply.
As alluded to above, the 900 hr limit is reached very quickly if rosters are designed this way. Most full time ww cc reach the 900 hr limit, even with generous MTB provision, so this is most likely to be teething troubles with the setup of MF, very similar to what happened at SFLGW.
I very much doubt that BA will roster MF to 900 hrs in 8 months then terminate. BA see MF as the future. How many crew would they recruit with practices like that?
What this does show is that in the real world, there are few absolute guarantees and protections. Maybe it will show a few old contract hardliners how good their deal still is.