Im kinda have same problem as OP (if you going self-found SP) that you tend to complete random set rather than your current build (like last patch, i got full bowzon set for like in many years?). So if I wanted to utilize that i would make a new bowzon to use it.
Usually by the time you found with your current char, you probably already reach 500 signets eaten, couple of SSU, couple of elemental RW and maybe full set of great rune. It depend on how un/lucky you are.
Im however though, do hope for more option in the future to reduce the RNG factor in the game. Of course it doesnt to be powerful as normal drop. Example:
Create a set piece via cube (just like in d3 iirc)
You need first to find the base (lets make it harder like rare sacred base), cube with it specific amount arcane crystals (i have no idea how much, but lets just say this is last resort once you already have 500 signets eaten) and lastly, add some weaken stats to the item and prevent it from get cubed (similar to giftbox stuff, my suggestion would be capped it to 1 socket only)
So the end you get something like:
Rare sacred base + 5 arcane crystals (or 10) = random chance to find any set of used base, but it have 1 socket and cant be MO-ed.
*I wanted to suggest something like 1elemental stone-only RW just like normal RW / gemword but i guess it wasnt related to this thread.