Although many Zelinka guns use that vanishing rear pin line release as it suits line wrapping on top of the gun body, which is a feature of many Russian and Ukrainian guns, I would prefer something on the side or under the gun. In that respect the Pelengas Zelinka is good as it borrows the side line release found on their other guns.
Ah, they do? Yeah, I certainly wouldn't want it on the top. But given that the builders tend to use 1mm thread pitches it could be as simple as putting a 0.5mm shim in the kit. Or perhaps two 0.25mm shims so that you can orient the back cap as you want. As long as they haven't placed the o-ring groove too far back on the cap, then screwing it out by 0.5mm should be fine. As for the plug valve or the spring loaded valve, I guess that's alright, too.
I just went and looked at the Titanium Bazovsky you started this thread with, it actually has the line release on the side

. So, perhaps there has been a move away from putting the line on the top:
I just found a pic of the Etelis rigged, side line release, too - well, at least half of the line...:
I think the grip is interchangeable. Perhaps for an extra skinny one for thick gloves.
They also make a cheaper version in Duralumin (a hardende alu alloy) without power regulator (also side line release):
BTW, this gun is only about USD 140 and with power regulator only about USD 30 more (though the latter was at a discounted 20% price). And I think the barrel is still stainless steel. I am not 100% sure it still floats when loaded as I think the Ti guns do in longer sizes. It seems it is possible to get into Zelinkas at OK prices - if the shop will ship to you.
Finally, from Zelinka Techno here's a slightly different take on the line release with a linked traverse line release, but it is still operated via the sliding rod which retracts into the reservoir as the shooting barrel moves forward (also, notice this is a one of the reletively few rear handle Zelinkas):
It comes in a power regulator version, too: