I'm not sure I'm understanding your question correctly but if you're asking whether you can use 2 pieces and get half the bonus: no, you must use a full set of 4 pieces. 

I *think* he is asking Plarium to change it from a 4-piece set to a 2-piece one. If so ... my guess is that will be a resounding no

Solid guess imo :)

I hope more of the new sets are li protection and stoneskin with the flexibility to use 1 to 6.  

Fair assessment, and agreed. :P

Agreed with Trips too. Would enjoy more sets that give that option, but obviously don't think reworking old sets is in the cards. Though this would be a nice solution for some of the more useless sets, turning them into sets that offer entirely different bonuses that scale from 1-6 pieces. But I don't know if we'll ever see that in standard dungeon drops. 

Would love to see 4 pcs sets give half or even less(30-40% of its original 4 pcs value) bonus from 2 pcs , letting early/mid game player more freedom over gear while creating new possibilities for everyone else ofc .

Would mean using less broken set piece for stats because you didnt roll X yet ! Might be some work to implement but would be worth it for the player enjoyment imo .