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A 75mm would be a compromise, slightly easier composing and focusing, crop-able to 85mm, I do prefer 85mm and even then you might want SS if possible. 100mm is too long? Fast portrait lenses have strongly tended to 85mm and 100mm is for macros or macro-cum-short telephotos like the 100MP.
A lot of people are like you, douglas, and use one only now and then. With travel good people shots are very sweet - if you get it right, I think the AF is good enough now - I see very few misses from focus error even at ISO 8000 in the RX1, pretty amazing to me. You do have to watch focus fade closely. A tele should be easier on AF?
I'd see an 75/85mm 'RX2' as something valuable long term, imagine a Zeiss version of a traditional low element number (updated and optimised) of a 90mm Summarit-M f2.5, something like that and with real character. Better if a short MFD too. Corners are easy design-wise too, to take full advantage of the sensor.
An RX1 body with same size lens in that FL area, yes please. I hate pointing large cameras at people and watch the natural demeanour and behaviour evaporate as they see this huge device, looking vaguely military and black, pointed straight at them and making weird clanking noises from AF and mirror and shutter. They feel like they are appearing on TV.
Most people can't afford that kind of Leica M setup, and want AF in any case. Small AF lenses that work well are very good things for many users.