Its the future.

Seriously, as EVFs improve there's less compelling argument for the whole pentaprism-focus screen-mirror and mirrorbox route. dslrs aren't going away but they're now as small as they're ever going to be, and eliminating those bits opens the door to shrinking both camera and lens without giving up performance. Hence, 4/3.

A shoutout here to digital interchangable lens rangefinders, but since the $8000 M8 is the only one sold at present (lens extra) they're not exactly setting the world on fire. The fixed lens Sigma DP1 is another nice backpacking option, but that fixed lens is a big shortcoming for a nearly thousand dollar camera.

The Panny G1 has been very well received, and Oly is rumored to be releasing two 4/3 bodies and an unknown number of lenses later this year. One body should be similar to the one pictured (a mockup from last summer's Photokina) and one will be a more complete camera that will include a viewfinder of some sort. A remaining question is whether Oly will offer in-body IS or make it lens-housed. I'm hoping for in camera, like most of their dslrs.

Panny's 4/3 lens roadmap shows great promise, especially the ultrawide angle 7-14, which will be miniscule compared to its slr counterpart. Tiny, fast primes could come as well.

http://www.dpreview.com/reviews/PanasonicDMCG1/images/features/roadmap.png

Video fans will rejoice, as it's much easier to put video into these cameras than into dslrs.

If the economy doesn't torpedo these efforts at birth, I fully expect large numbers of lightweight backpackers to abandon their dslr kits for 4/3. They're game-changers.
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--Rick