I'm really exited by the recent announcement of the Fujifilm X-Pro 1. It's really very close to what I personally would want in a general use everyday type camera. The Leica M9 is too expensive for me and I think is overpriced for the overall level of functionality. Fuji X100 has a fixed lens so is very limited. Sony Nex-7 is almost too small and lacks dedicated buttons and good ergonomics.
One of the major reasons I like these new rangefinder style cameras in particularly vs. SLRs is the very small distance between the sensor and the lens which allows the use of adapters for using virtually any lens made. This can also be particularly useful if you have already invested in a professional Nikon or Canon system as you can utilize those lenses. However I still see a tendency to compartmentalize functionality of cameras by types which is no longer needed with current technology. You can already see this type of thinking is slowly breaking down as Video SLRs are now being seriously used by professionals. However I would like to see the barriers broken down completely which will happen in the next few years anyway.
What I would like in a camera is a rangefinder style design but not trying to copy all the details of the old aesthetic like Fuji is doing with the X100 and X-Pro 1. Leica started to come up with a very beautiful modern aesthetic with the Titanium version of the M9 (although I don't care about the Titanium part and it's way overpriced like most Leica stuff) For reference I do find the X100 to be pretty but the X-Pro-1 to be a bit ugly in comparison; the Titanium M9 is drop dead gorgeous.
Weatherproofing like the Pentax K5, Olympus E3/E5, and Pro bodies from Nikon and Canon. Once you get into the price range of the Fuji X-Pro 1 and certainly the Leica there is no reason not to include at least some weatherproofing. There is no reason I see that rangefinder style cameras have to be delicate. (compared to SLRs) Obviously this is going to be limited by the lenses you use.
I see no reason not to have most of the advanced movie mode functionality of the high end Canons for example in a rangefinder size body. Processors are getting powerful and small enough this shouldn't be too big of a challenge. Sony Nex-5n and Nex-7 have about done this. Also they now have a pellicle mirror adapter for use with their A-mount lenses that allows their compact Nex cameras to have the super fast focus and high-speed continuous auto focus with video of their newer SLR's. Now if Sony would design the technology and have Fuji design the interface and have Leica in charge of the overall aesthetic and put into one camera it would be close to perfect, lol.