I like this idea. It sounds a lot like a Snelgrove method where you use the heat of the bottom colony to keep the split warm. Is there some reason to use a QX instead of a double screen board? Are you trying to draw bees and resources up to the split? I imagine that if the bees can touch, then the bees might not know they are queenless. How often do you get a failure to requeen in the lower colony?This is my method, though not easy it works. I locate my queen and take the frame she is on and two more brood frames and put them in a separate brood box. Replace the three frames in the now queenless parent hive putting the replacement frames on the outside. I then put an excluder over the parent brood box/s and put two supers on top of it. A colony not having to feed brood collects a lot of honey! I place an excluder over the supers and put the split on top and provide it with an entrance of its own. The parent hive with its wealth of resources builds quality emergency cells. Ten days after the split, I can harvest surplus emergency cells if I wish. Mostly I just let nature take its course. Then I leave them alone for a month unless it has been a big honeyflow and I needed to add a super or two and that happens. Then after the month, I come and set a bottom board beside the stack and put the split which is now a full single that may have supers on it, on the bottom board. I just reverse the stack until I get to the bottom brood boxes. If I find a queenrite colony I move the supers back on to the hive and add more because we have a strong hive and my main flow is just starting!. My single on the bottom board can then have a second brood box added and supered later as required. Or, I tend to just pile on supers and produce it as a single until the main flow is over. Then I pull the supers, add a brood box of drawn comb and feed it full for wintering.
If the bottom colony failed to raise an emergency queen, I set the old queen and her single on top of the bottom honey heavy brood box and store or extract the other depending on its history and stack on supers. You win either way because you had perfect swarm control and didn't have to buy commercial queens that live five or seven months.