I would like an SLR that uses CF cards and either a Canon or Nikon mount.
I would like the sensor to be modular so it can be upgraded or changed to meet you needs. You need an IR sensitive/balanced sensor for art or astro photography, then swap out your regular one and put this one in. You want a little resolution but far less noise, put that sensor in. How about a sensor that will "pan" across frame so you can get weird distortions like old focal plane shutters would give, put the sensor in.
I would also like the OS to be modular and open source. Right now my camera literally runs DOS, complete with cmd.com. I would like the os to be open so people can write modules for the camera and you can use the features you want, and leave the others off. Like flash exposure compensation, or different auto focus algorithms, or even artistic filters to run the image through. Maybe a module you could load in to let you do time lapse photography. Or automatic watermarking or encryption? I think the biggest module market will be for usb drivers for networking your camera or writing instantly to external storage devices.
As we've seen with the hacked firmares for cameras, there is a lot of stuff the cameras can do that manufactures leave off. I think it would be awesome to see cameras become more like computers where you can upgrade the sensor or the memory, load different OS's, and basicly give users the options to tailor their camera to meet their needs and budget.