I have asked Sennheiser's chief wireless engineer for a 1 rackspace integrated IEM Tx and Rx in one chassis with compatible frequency co-ordination and in typical German fashion he replied "Why would you want that ?" [...]
I suspect the reason he's sceptical is because, from an RF standpoint, this is actually a pretty tricky problem. Putting a transmitter near a receiver typically causes the receiver to desens and have reception issues. On the rack side this can be solved with proper antenna placement (although at that point your antenna rig takes up enough space that the 1U form factor is pretty moot); on the performer side things start to get tricky, especially if you want diversity reception for your IEMs (which you do).
The Telex BTR approach to this problem was to leave ~100 MHz between the RX and TX frequencies and then use filtering to reduce desens to manageable levels, but with available spectrum reductions this has gotten a lot harder. A shared antenna on the beltpack and a circulator would theoretically work, but you'd again lose diversity reception (and circulators tend to be delicate and expensive).
Probably the best solution is the most common: put a large bag of meat between the RX and TX beltpacks to attenuate the TX signal at the IEM RX. Of course, this means using a single beltpacks for both isn't possible.
Basically, as I understand it, what you're looking for doesn't exist because of physics...
-Russ