Reflex, a new 35mm film-based SLR, is now out of the bag and approaching reality.
Basic specs are that the camera is manual focus, manual exposure (or aperture priority) via a spot/averaging meter, has a shutter that works from 1s to 1/4000 (plus Time and Bulb), and is a magnesium body construction that weighs in at 490g. ISO settings from 25 to 6400 are supported. Inside, an Arduino controller and Bluetooth (for metadata capture) make it a bit more modern in design. Indeed, the camera not only has a small flash (and a hidden hot shoe on the rewind lever ala an old Nikon design), but it also has a small continuous LED light.
But the big design point is modularity, which comes in two pieces. First, the lens mount is modular, and you can get M42, Nikon F, Canon FD, Olympus OM, and Pentax K mount modules for the camera. Second is that the film back is modular, too. Initially this means that you can buy multiple backs, load them, and switch between film stocks as you shoot (I think you lose one shot doing this, but that's unclear in the details at the moment). But I'll bet that we see a digital back for this camera if they successfully get it off the ground.
Which brings me to this: it's a Kickstarter campaign, though one run by people who should be able to get this to market.
Price for an initial unit with the M42 mount is about US$460 (it's a Euro-based company, so the 350 Euro price can fluctuate for us on the other side of the pond).
