For me the minimum requirements are indeed a system with interchangeable lenses and no mirror box, therefore a continuous optical viewfinder in combination with an electronic viewfinder. Yes, I want both.
The biggest problem to me is the format, sizewise I mean, because of portability, and of imaging possibilities. I did add a Pannasonic GF2 to the bag not so long ago, with a bunch of optics, but essentially that was a replacement with better IQ and more possibilities than my trusty old G10. It is not perfect, but it seems that the latest 16 MP m43 cameras are quite a bit better, and that was really the reason why I went this route, apart from the rather good and good range of optics and the good deal I got.
Ideally I would like a miniature FF system camera, no larger than my old Pentax-M series cameras, and AF not required as long as it has focus peaking and a proper rangefinder type focusing system (ideally both), which would at least bring the size of the lenses down to a more manageable level whilst being able to retain large apertures, a must for me from a creative POV - I do want and need thin DoF possibilities. As a temporary measure I wouldn't mind using my current dslr lenses, with an adapter of course, but ideally I would like to downsize my carry-all drastically, without compromising IQ and possibilities. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
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IOW, I really want at least Canon 5d MkII IQ in a much smaller package without mirrorbox, and smaller but still fast lenses, essentially the optics of my current lenses without the bulk that AF adds <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
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I would like for someone to establish some kind of standard lens mount for this as well. And other than that, I would also like other manufacturers to adopt the m43 standard, so we would have two standards for CSCs. I think an APS-C CSC is a waste of time, as lenses are not going to be (much) smaller than lenses for a FF CSC, and going smaller than m43 impacts just too much on IQ, IMO.
My 2 cents <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
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Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....