Ilya, where are you getting these great pics, may I ask?
My concern about this design is that it, like all open-bolt designs, is going to need a new trigger group to make it semi-auto. OK, that can be done, HOWEVER... where do you put it? The bolt carrier on this one is upside-down in comparison to an AK. THat makes it out of reach for a normal AK hammer. That's where it gets interesting. We can't use a REAL LONG hammer because the recoil spring is in the way! SO, I think something could be done to take an AK hammer and hang it upside down (from the top), and make an AK style trigger & sear that is REAL LONG to grab the hammer. I'm not sure how else to do this - yet. THAT will be the real challenge!
I wonder how the semi-auto M-60 MGs are built? There may be something there we can draw from.
Also, I think a brand-new firing pin will be needed too - I see no way around it. The existing pin is stationary while the open-bolt-firing bolt carrier drives the bolt home. Therefore, the factory pin is way too short for a hammer- or striker-fired closed-bolt design. I think the bolt is too long for an AK firing pin, however I have a lathe so I'm not too worried. I'll sacrifice a grade-8 bolt in the name of a PKM firing pin