i called black dog machine out of idaho last week, they suggested that if we wanted something like that, the best bet would be to work with the manufacturer, (suggest they buy BDM mags to ship with whatever 22 unit we talking about) she said (Rachel at BDM) that during some of hte panic years SIG would buy thousands of mags a WEEK to include with their sig 522 guns...
with that being said, i am not certain cz would be keen on htat. buuuuuuut, if the possible hi cap mag could be as reliable (or more) (not that BDM mags arent reliable mind you) as the current, mag welded in side another mag setup (time intensive much?!??!!??!!?) then they could spend more time building the guns/parts instead of mags. possible higher profit margins as well?
long story long, i ordered an UZI 22lr mag from BDM, and i am fairly confident i can mod it to run in cz75 kadet, about to go try stuffing it into the p07 magwell. its a 30rd'er, and has a long straight section, just need to work on adding some metal feedlips ( thinking aluminum, screwed to the housing, ever so gently).