Re: Mass market?
OK - so how does the software cope with differing resolutions?
By not using pixels as a measurement unit. Same as any other system with varying resolutions. Ideally, you want -1 to be one edge of the screen, +1 to be the other edge, and the origin (that's 0,0) in the centre. Or you can stick the origin in one corner and have (1,1) be the other corner. Use whatever relevant system call to detect the screen (or canvas, window, whatever) resolution when you start the application up, and create your OpenGL viewport based around that. Aspect ratio is detectable by just doing width/height. Adjust your UI accordingly.
If you're on a platform that allows window resizing, then attach a function to whatever on_resize event the system has, and have it reconfigure the viewport accordingly.
At no point do you ever want to be measuring distances in your 3D scene with pixels.
Same as everything else, again. There are plenty of test screens that will give you a reference while you twiddle with brightness, contrast, gamma, RGB/colour temp.
different CPU/GPU specs?
Same as every other platform. I already have apps on my phone and tablet that have a "Tegra" edition for extra shininess on Nvidia's chips.
differing accelerometer sensitivity?
One-time calibration. "Put your phone face-up on a flat surface. Now put it face down."
memory limits? differing OS builds with jitter effects from different interrupt handlers?
Oh now you're just trying to think of problems, aren't you? These were all solved some 30 years ago. Just use the 30 year old solutions, like various Android devs seem to have been doing already.
Really, I don't get why people are complaining so hard about the Android "ecosystem" being fragmented, when plenty of people have been developing for quite long enough in the far more fragmented Windows environment.
Don't forget that this is basically just a set of fancy goggles that you strap a phone to. So long as your app presents two images side by side, and has the virtual cameras spaced appropriately, it looks pretty much like it will work.