I'd be interested to see the numbers showing that re-brigading the RAF would save money. Army HQ constantly grumbled about the running costs of JHC, they'd shed a track if they had to stump up for ownership too.
But more importantly, I'd like to see it demonstrated that the Smuts Report is no longer valid. The RAF was created precisely because the RFC and FAA were incapable of using and getting the best out of this new fangled capability, air power. I've not seen any evidence to suggest that has changed over the years, if for no other reason than air power isn't foremost in most Generals' and Admirals' minds. So I suspect you can't effectively demonstrate the rationale behind the 'founding charter' having changed sufficiently to warrant re-brigading.
Additionally, there would be no cost savings by re-brigading the RAF's assets and responsibilities. The kit and personnel requirements wouldn't change overnight just because we are wearing a different hat, and there'd be no savings from rationalising 'top brass': the Army and RN are too busy running their own services to take on a new one, of which they have limited experience, within hide. You'd have to take your expertise with you. That's assuming personnel agree to go to the other services.