The idea is to keep people in HMFC until they've acheived the qualifying total. At that point the choice will be theirs, but they should then be in range of the next retention inducement which would be financial.
It takes those who fly high performance aircraft quite a while to achieve 2000 hours; bear in mind that those hours are rather more busy than many airline hours! Hopefully HMFC can retain people until roughly their mid-30s, then it'll be their choice to stay or go. The individual will benefit from a second career option and the airlines will benefit from a source of experienced and competent aviators. The numbers will not be huge, so there shouldn't be any impact on the entirely self-funded youngsters. But I don't know of any military pilots with ATPLs who haven't been snapped up by the airlines when they left.
Interestingly, any company which asks for your age when you apply for a job with them will have to explain why they need to ask the question; age discrimination will soon be illegal, so companies with a concealed 'age limit' for applicants will have to revise their ideas.
In a few months' time, certain airlines may find themselves being asked whether they would be interested in employing an ex-military senior training captain A2 QFI/IRE with 4-5000 hours 4-jet command time on world-wide routes. Not that I'm considering leaving myself, but if age even enters the conversation, they'll be asked to explain themselves!
I understand that the usual method of applying age discrimination is to hide behind the facade of the 'human factors' selector's assessment and to come up with a spurious reason for rejecting the applicant on such grounds - which are never disclosed.