Ken & Matt,
You guys are making me think....and that can be bad. :-)
Now I'm thinking like you, TWO turrets. 50+80+105 (35mm+6x6+6x9) and 135+150 (4x5) or some variation of this.
I was talking to one of the guys at the local photo shop and rather than the MF and LF enlarger setup that I had been thinking about, he suggested 2 LF englargers. Just set one up for 35+MF and the other for 4x5. That way I still have the option of going to 4x5 on either enlarger if I need to. And the baseboard of the 4x5 enlarger isn't that much larger than the baseboard of the MF enlarger. Then what to do with the MF enlarger? Oh more decisions...