I do not believe that BA cabin crew in the future will only be able to afford public transport, using a laundromat, or living in a rented room whilst the company makes huge profits.
What sort of people will be attracted to a job like that?
The market will find the right rate.
Why are many thousands of hopefuls for a BA CC job apply?
At what point will this diminish to none or even reverse to people leaving in droves as the wages/allowances/perks are cut?
The right rate for the job is when an employer can fill the vacant positions with ease and at minimal cost.
If the wages/allowances/perks are too low to attract, then they have to improve. Quite simple really.