Owners Pondering Idea of QBs Having Separate Salary Cap

That's not how the NFLPA thinks. The answer to them will be to raise the entire cap, not cap the amount QBs can make.

And, I'll note that the top WRs are now making what the top QBs made 5 or so years ago so putting a limit on QBs isn't going to change anything because all positions will eventually rise to a level seen as "just too much". Except it isn't too much because the NFL is making that much money.
The NFLPA reached agreement with the NFL on limiting rookie earnings to shift more money to other players, I don't know why they couldn't do the same with an individual player cap. I think they would balk at specifying a position since it would open the door to one position having a ceiling that gets surpassed by a player at another position.

If they could negotiate for increases in salary minimums (or benefits) for the other 52 players on the roster to keep the owners from pocketing the savings, it could work. They could also push for an increase in minimum cash spending to accomplish the same goal.