I am led to believe from long time cabin crew friends, that the Company already do this with the cabin crew, but in different circumstances.
If they become unfit, often the cabin crew rosters will change to give them another pattern after the period of unfitness, and this pattern eats into what where previously G days.
Has been like it for years, and they just accept the company stealing their G days to make up for the temerity of being unfit for work.