>>64272054 (OP)
There was at least one prototype helical magazine for the PPS-43, and supposedly also the PPSh-41 (though trying to find an image of it after COD is annoying).
Could certainly be done, though I assume they felt it wasn't worth the effort for the sidegrade, also the variable tolerances of the PPSh-41s magazine wells and magazines probably made it particularly less worth it.
>>64272103
It's easy to meme on the Norks, but helical magazines have been done for .22LR, 9mm Luger, 9mm Makarov, 7.62x25mm Tokarev, and Calico have at least experimented with .40 S&W and even 12-Gauge.
There's no reason it couldn't be done, but helical magazines are always a complex matter, so they may not necessarily work well.
>>64272642
Pointed doesn't have to be a problem.