This is the absolute #1 thing I NEED (I already have all the other upgrades, and those are just wants ) - I’m just guessing here, but I would bet that this might not even be too long for me. I am 6’3" and have a unusually long LOP.
Back on topic though, and this is a fair departure from the general idea of the thread - but still on topic…rather than an adapter for collapsible AR style stocks, why not a stock specific for the s2k that takes advantage of the locking pin that the carbine already has? the same one that is used to adjust the current butt section. It seems to me that the current longest LOP is likely to short for even the shorter end of the LOP spectrum for average shooters - for a truly “good fit” LOP that is, not that we don’t all make it work.
If we, you rather, just built out a poly butt section that was longer in general, ie just “tube” where it contacted the actual bolt tube, and then some distance behind that was the actual stock, I think this is really what we all need. It also allows us to design around all the constraints. the top portion can be cut out to allow the locking mechanism to still function when folded, and to give clearance for the front site post when folded.
This sort of setup would also allow for many more positions than just three, in addition to longer overall LOPs. So, similar to the AR collapsible style, just not as quick to implement changes - though I would hazard a guess that most of us are not regularly meddling with our AR stocks either…