The PMR-30 conversion is possible because the .22 WMR barrel lifts out and can be replaced easily with a .22 LR barrel. There is a decent chance that Kel-Tec can make a double stack .22 LR magazine with the same exterior dimensions as their .22 WMR magazine.
The SU-22 uses a fixed barrel. Replacing the barrel is a factory upgrade, and not an easy thing. You certainly wouldn't be able to switch back and forth with a caliber conversion in the field.
Similarly, the Ciener style .22 LR mags that have the same exterior as an AR-15 mag made the SU-22 practical because Kel-Tec didn't need to make their own magazine, which is a tricky thing. I don't think there is a .22 WMR magazine in an AR-15 form factor, so that would add a lot of development to the SU-22WMR project, and I doubt the market demand would support that effort by Kel-Tec.
Based on the number of cool new gotta-have-it firearms Kel-Tec has made recently, compared to their comparatively lackluster ability to supply the demand they've created, I think most Kel-Tec fans would argue in favor of them putting more effort toward manufacturing their stable existing lines, as well as the PMR-30, RMR-30, RFB, and KSG. Few people would be encouraging them to spend all the time and effort that would be needed to create the SU-22WMR... particularly when they have the compact, high capacity RMR-30 coming out just as soon as they finish it, and most of that work is already done.
