I know someone who has tried this idea and they gained half a horse power. On further examination they put down the extra horse power down to the gudgeon pin as it was shorter and not flexing as much. Half a horse power is not much but the engine is 50 cc and they want to break some speed records with the engine.
This idea is a very old idea just like the shift camshaft on the new BMW engined bikes.
As for the First Pix with the Screw top piston. I have a Russian mfg'd Engine A wee 2 stroke designed for Control line combat. Yess a toy engine. It is a Marvel of ingenuity and machinists skills from mid 90's. Turns ~35 k rpms in use so not so toy like. It features a Moveable piston height via it's screw in wrist pin assly and specific spacers. This allows timings changes coupled with compression changes via it's screw on head. A seriously tuneable to current needs engine Very nice. BUT and it's a critical 'but'... the piston carrier tends to unscrew itself. The variable design was not continued in subsequent developments.. for learned reasons
IMO a couple of kids in some wee shop in darkest NZ are pissing up the wrong tree with a screw top piston and it's reversed Dykes ring.