IMHO what Doug asks for is a bit of a contradiction by definitions UNLESS we can agree that a Critical Listening Room is a Critical Listening Room. We try to design ALL of our control rooms, mastering rooms, production rooms, etc. (listening rooms) as Critical Listening rooms. We also try to optimize the "main" monitor situation for each design, be that a $60K pair of Free standing mastering monitors, or a pair of un-listenable compressions driver 2-way double 15" in-wall mains...
The basic acoustic approach IS absolutely the same for both types of environments. The client has to decide what is the best scenario for their setup. ie: in-wall vs: free-standing monitors, console vs: small computer setup.
I understand the "issues" with a large format mixing room vs: a minimal equipment mastering setup, BUT as we approach the ideal synergistic "comprimise", can't we hope that clients can find one setup that just works??
We also design loudspeakers and we don't feel that there is any difference between a mastering environment and a mixing environment with regards to monitoring.. You can have it free-standing or in-wall, but what you want is accurate, low distortion, high output monitors that can handle either assignment. This is how we look at Griffin monitor installations... EVERY ONE is a Critical Listening Environment and we would hope that at least with regards to the monitoring that a talented mixer would be very comfortable mixing and an experienced mastering engineer would be equally comfortable monitoring his work... (of course some blind folds may be required to get past pre-conceptions).
The specific scenario originally proposed concerning a room with "two ends" is riddled with difficulties at first glance... How to deal with a large window at the front of the mixing position and rear of the mastering position. How to work out good geometry and proportions for two "sweet spots", how to handle RFZ and diffusions requirements for both listening positions..... But, it's really not that much more difficult than properly and completely considering a proper 5.1 setup. We always try and treat the surrounds as equals instead of orphaned step children in our surround rooms. This can be difficult and possibly impossible in some site line scenarios.... Look, anything is possible... I would think a rather large room would be a good starting point. Possible a "false" rear wall could be installed a divider between the two positions and offer diffusion for both sides? there could be many other approaches.
Actually, it sounds like a really interesting and unique project. Doug, if you're serious about this, I would be happy to talk to you about it.. It wouldn't be cheap, but neither is the equipment requirements for such an installation, so.....
Anyway, that's the way I see it.... good monitoring is good monitoring and a good room is a good room... what you put in it, basically just messes things up and it's our job (as designers) to minimize the acoustic clutter caused by the gear, and give the user the ergonomics they're looking for. This type of project is no different...just bigger and more involved...
Sounds like fun!! when do we start??