The Sony NEX mount is larger than a Leica M-mount, which means a Full-frame is on the way too, even with the reduced flange-back distance. They will probably do it through a combination of lens optics and sensor micro-lens offsetting. Remember that the old Sony DSC-R1, with its 1.68x near-APS-C sized sensor, used to have the rear element of its 14.3-71.5mm f/2.8-4.8 lens, positioned just 2.1mms (that is millimeters) from the sensor plane and the R1 had absolutely ZERO vignetting or other aberrations.
Also, even though these initial models (NEX3/5) are consumer oriented models, the "NEX7" that is expected to be announced in September, 2010, will come with buttons/dials galore, built-in EVF and also a built-in body-based Image Stabilization (which will be firmware controlled to switch off when IS lenses are mounted - especially for video).
Sony, going by their Alpha designations, have designated their consumer-grade models with the 2, 3 and 5 designations (NEX3 and NEX5 being consumer models). The NEX7 will be a semi-pro model, with the obligatory dials/buttons but will come with an APS-C sensor (a more advanced version of the NEX3/5 sensor). Their NEX8 and NEX9 can be expected to be the Full-frame models.
I would not be surprised if a Panasonic GF1-sized Full-frame NEX9, with direct user controls all around (buttons and dials) being released, with a few high quality Carl Zeiss Auto-focus primes. Remember that since such a format does not have to contend with a swinging/flapping mirror, the wides and the ultra-wides in turn do not need huge retrofocal designs and we are essentially looking at a Full-frame 14mm f/2.8 PANCAKE, with the whole thing (camera + lens) weighing in at 350gms - unthinkable for a dSLR ! We are essentially looking at such a Full-frame camera model, with a 14mm f/2.8, 24mm f/2.8, 35mm f/2, 50mm f/1.4, 85mm f/1.8, 100mm f/2 and 135mm f/2.8 fitting into a tiny bag - again something that is incomprehensible in a dSLR based system. Video begins to make a whole lot more sense than when executed via kludgy dSLRs.
These NEX3/NEX5 models are definitely the start and I predict will shake up the marketplace a lot more than the micro-4/3 (which are "condemned" to perpetuity with their smaller sensor size and larger-than-needed flange-back distance which will make the bodies inordinately thick) models have.