By moving to electronically controlled aperture, you remove any remaining mechanical design constraints on the lens design. As has been stated elsewhere on this thread, it becomes easier for 3rd party manufacturers to adapt their lenses to fit. It's also useful for Ricoh, as it may be easier to keep lenses compact and/or allow novel designs.
A Sigma rep recently told me that the aperture lever was a barrier (along side lack of predicted demand) to offering many new products in K mount. I hope the KAF4 mount will encourage them back to the market with products that complement the Ricoh line-up.
I would also expect any future Pentax D-FA releases to be KAF4, as the K-1 will be compatible with a firmware upgrade. What I would not expect is for any K mount DSLR camera to lose the mechanical aperture control. Ever.
The term "Pulse Linear Motor" seems slightly wrong if the diagrams from
Ricoh Web Page are to be believed. I think "Pulse Linear Actuator" is more accurate; the motor is still rotary. There should be no worry of lens rattle – this is not the same as the truly linear “voice coil” actuators in some m4/3 lenses. There may be advantages of using the pulse (stepper) motor design for focusing when a specific position of actuation is desired. Eg the autofocus determines that position X is roughly correct and commands the motor quickly and precisely to that position, where final focus finessing can be measured and commanded. I’m not sure PLM will find universal application in new lenses.
I would say that overall these features indicate further proof of Ricoh/Pentax planning for the future, which has to be a positive thing.
:-)