Originally posted by pathdoc No. Not until the PLM aperture drive has had a few years in the field to let the potential bugs get sorted out. The first order of business is to put the PLM system into a wide-normal consumer DA prime (say, a 17 or 18-55/4.0) and give the K-30 or K-50 user something to fall back on if their aperture block dies.
In addition, the Limited primes do not need any more gadgetry stuffed inside their shells than is already there. Their strong suits are image quality and COMPACTNESS, and the latter would be ruined by ramming a DC motor and aperture control system inside.
That being said, we do need a modern D-FA fifty to go on the K-1; if you want to propose an HD D-FA 50mm f/1.4 DC WR PLM lens as a replacement for the venerable FA and even the DA*55/1.4, by all means. But the decent thing to do is to ensure that the K-30 and the K-5 series have the PLM firmware fix first; if the K-50 has it, they should too.
I agree with the basic idea of being wary of adopting untested technologies, but can they afford to wait too much? You say "a few years", I'd say "as soon as they're confident it's working". Hopefully that means 2017
I think Pentax should generally do away with both screw drive AF and mechanically linked apertures. The ideal D FA Limited, for me, would have in-lens motors and be WR; it should still be quite compact due to a smaller than f/1.4 aperture. For non-Limited lenses, I see no reason for still using the in-lens AF motor.
As we go back in time, to older and older cameras, the probability of users buying relatively expensive lenses decreases. I'd be pleasantly surprised if the K-5II series will benefit from a KAF4 upgrade, too - as it's the first Ricoh Pentax K-mount flagship.
Besides, the old camera users could get the old lenses, if they didn't already. We shouldn't set artificial limits on progress based on cameras launched a decade ago.