StewM,
Don't worry too much because, as I have mentioned, I don't think any airline like BA would want to roster any crew more than BA are already rostering you Mixed Fleeters.
It would be self defeating to have exhausted crew because exhausted cabin crew don't give good service and in my personal view some of the rosters I have seen (not all) have been shattering.
The Man and Ams have been added to help with your hours and also to help keep you productive because they are used as links at the beginning of shorthaul trips and at the end and as you have mentioned the flying hours are lower.
One outcome of this legislation might actually help all crew that operate longhaul rosters like you and WW crew is that the 900 hour would go. I really don't think you need to worry that your rosters will get worse from this because you are all very productive already.
Ultimately I expect that Unite will obtain the right to negotiate for you but seperately to WW and E/F just like they do for SFG, but that wont be untill some kind of settlement!!!!
Hope that puts your mind at rest. I find that you get quite a lot of scare mongering on all forums from one side or the other, so please don't worry.
BG
These are my own personal views and no those of BA.