What I honestly think would be the best is if some manufacturer actually made a 'modern' rangefinder, as opposed to making a digital version of existing rangefinders. All the digital rangefinders lack even the most basic features found in other styles of digital camera due to a strict adherence to tradition. The existence of the rewind crank is one example, and people complaining about the lack of a frame counter another.
Someone should make a completely new rangefinder and say **** all to tradition and just make a great rangefinder, instead of being boxed in by the past. Even starting small like making frame lines illuminated by leds, making the framelines consistently bright in all conditions with nearly no battery drain. Capability for multiple frame lines for a wide array of lenses (one set of framelines up at a time, determined by lens selection in a menu; m mount adapter for failsafe), perhaps an adjustable magnification viewfinder.
Hell, at one time the M5 was an outcast, with it's larger size, it's incredibly accurate meter, it's 3 lugs. Every now and then you need a model to cut through the wilderness and lead the way for the future.
I'm happy with my M2, and I won't be using a digital rangefinder for a long time (due to exorbitant prices coupled with no real significant improvements over the M2), but really, shouldn't rangefinders be afforded some sort of progress?
Edit: I know the led framelines or whatever might be a silly idea, my point is that the developments in the core of rangefinders essentially halted years ago. We don't have better viewfinders than we did 20 years ago, better focusing patches (some point out that the M8/M9 are harder to focus with fast lenses than their M2/M3 counterparts), or any improvements of the basics. It's somewhat sad that a 50+ year old camera can be considered superior to it's modern counterpart. Note that this isn't ad antiquitam.