I travel a lot, and my dream camera has always been a light, large-sensor body with interchangeable lenses. The goal is to carry two bodies, and a set of high-quality zooms and perhaps a couple of primes, plus needed camera accessories (battery chargers), plus a laptop with necessary accessories (power supply), in a carry-on bag that would also hold regular travel stuff -- extra eye-glasses, pens, notebooks, a novel, etc.
All to fit in an overhead, even on smaller regional flights. The m4/3 systems are very close. I have both a G1 and an E-P1, which, in their differences, and their abilities to use the same lenses, are complementary.
I no longer think these will be supplanted by the APS-C systems, because I'm not sure an interchangeable lens system can be made much smaller than the Pentax K7, even if a builder went to a EVF. I have a Nikon system for heavy-duty work with both a D3 and a D300. If you put a G1 next to a D300, you can see that it is definitely smaller, and lots lighter, **but it's not way, way smaller.** an APS-C with an EVF will fall someplace between those. The larger sensors also inherently require larger lenses.
The upshot is, the m4/3 system is a major step for travelers and other people who need a high-quality, but lightweight system, and I don't think APS-C will be able to encroach on that...the K7 may already be approaching the lower limits on size for a full-function APS-C camera.
I'm also intrigued by the idea of a removable, but full-function EVF for the rumored new Panasonic. Again, it makes it easier to pack and to carry, and gives you options in use.
The big drawback to using both the Olympus and Panny cameras together, for a traveler, is that the batteries are different, and you have to carry two bulky chargers. I wish the m4/3 spec had included batteries...
JC