I have and have had Oly DSLRs from as small as the E-410 and E-510 to as large as the E-3, and also have the E-P1 Pen; and I will say that there is absolutely no comparison in size between the mFT and FT. So yes, I do believe the market is still strong and the Olympus DSLRs, even being the smallest in the world, will never come close to the compactness of a Pen.
I haven't done it myself yet, but I've actually given my E-P1 Pen to another photographer on a location shoot, slapped on a High Grade Zuiko lens and hooked her up to the lights to shoot an entire full day model shoot.
The photos turned out great, though of course the shooting was weird for her (as it would be for me, which is why I don't do it).
It really is great having such a capable camera in such compact form, which can even be used as a professional backup if need be (as long as you have an adapter for your lenses). However, the lack of a viewfinder was the big deterrent to actually using it as such... which the E-P2 appears to address as did the Panasonic GF-1.
My E-P1 travels with an FL-36R hotshoe flash AND diffuser everywhere, and it still fits in a tiny bag no bigger than I've seen anybody carry a G10 in. The EVF really was the big thing missing, in my opinion.
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