I don't know about perking ALL planes except early war ones, but
I could definitely see lightly perking later war variants of plane and leaving the earlier variants free.
There are alot of planes to fly in AH, but most people chose the best free plane they can get (a rational decision), hence the hordes of LA-7s, N1Ks, Spit IXs, and P-51Ds.
It would be interesting to see what happens to planeset variety if HTC expands the number of perked planes but keeps their cost low.