There are a couple of hypotheticals at play here. Your bees may be superceding your present queen as you say you have seen a supercedure cell that appears to be ripe, but then again, you mention your queen is laying her little fanny off.
She has lots of worker brood? Very good solid pattern? I would suspect if this is true they wouldn't try and supercede her.
Are you certain you're not seeing swarm cells? What you described was a supercedure cell, but I am confused by what you are reporting.
If they supercede your queen and make a new queen and you place a queen excluder between the two deeps, and your older queen starts to fail and they supercede her, you could wind up with two virgins awaiting to mate, or one queen and I don't know about this scenario because I have never been there, just a guess, if one queen doesn't add up, the bees could leave one set up for the other, by simply going through the excluder. Old timers can fill in the blanks here.
If I were to set up a two queen system, I would start with two mated queens, but this is me.
Since you like to experiment, you could really have some fun with this, at the very worst it could be a really good learning experience for you.
And yes, you could always remove the excluder and let nature take its course.
I look forward to hearing other replies, very interesting post.
Decisions, decisions. ;)
...JP