What exactly does "capturing a Queen for free" entail? As in, if you capture your opponent's Queen without your own being recaptured during either your opponent's next move or within a number of subsequent moves after that, you'd win?
If so, this is almost indistinguishable from those chess games where a disappointed, begruntled player resigns after losing his/her Queen, or perhaps a Rook due to a blunder.
Well, you also have to consider that OP mentioned capturing a Queen for free. I think that was one of the main descriptors for his/her variant.
YEAH. That was it.
In positive news, I think if we added a few more descriptors and created a few more rules, it could potentially be a nicely interesting variant.
Until then, however, I'm going to pass. Since many my opponents and I sometimes/typically resign when we lunkeadedly lose our Queen. 
ok we can stop chatting here bc this all a -1inducing idea