Think I'll stick with the tried and tested 5mm felt under the keys within the housing.
Old dogs, new tricks etc.....
Yes, good enough, but have to remove the felt if taking finger board off again? Or remove the buttons?!
True, but how often would you be likely to want to remove the finger board? Probably only if a spring breaks, but hopefully that won't happen with any regularity.
If it should be necessary to remove an underfelted fingerboard, I've found the best method is to release the 4 tiny key frame screws so that the entire mechanism comes away along with the fingerboard. Then there should be sufficient clearance then for angling the keys to extract the mechanism from the fingerboard without having to remove the felt. (I certainly would not recommend removing the buttons!)
I use a fairly stiff felt, cut to a snug fit, so only a small amount of glue is needed to keep it in place, which can easily be cut through with a blade anyway should removal be necessary.
Please understand that I'm not claiming that "my way" is better; your idea certainly has merit, and kudos for thinking outside of the box. It's just that after 35+ years of successfully doing it that way, I can't see me changing this particular job at such a late stage in my box-fixing career. However, there have been a number of "improvements" described on this site which I have adopted, so my mind isn't totally closed to new methods....