Originally posted by RonHendriks1966
I'll buy that once they have found at least 20.000 customers who are satisfied with such a system and say it is reliable.
In principle, it shouldn't be all that difficult to engineer, although cost and weight are other matters again. The collapsible mount itself could be a short precision lead screw, to minimise deviations from the optical axis. Even the electrical connections and the screw-drive (assuming it was retained) wouldn't be big challenges. An interchangeable mount, though, would be something of a challenge, but is probably only necessary if an increase in throat size is required. There would have to be a system of signalling that short or long-registration lenses were attached, of course, but that would just be an extension of the present system. Sealing would be straightforward, too.
From a design standpoint, though, I would have thought that a dedicated removable supplementary lens in a mirrorless standard-registration K-mount would have been a more economical proposition, and give users the choice of APS-C or 35mm FoV to standard mount lenses. That, of course, is just about the body, and designing new short-registration lenses may be more economical than re-designing old standard-registration ones.
What a short-registration K-mount would provide, however, is the opportunity to provide smaller, faster wide-angle lenses than the current retrofocus ones, which may be an incentive to consider this dual-registration mount. Pentax is, if nothing else these days, about lightness and weather-resistance.