Anyone's guess what comes next- Omnivision no longer lists the current R-Pi sensor OV5647 on its sensor selection web page http://www.ovt.com/products/category.php?id=11
but that page does list seven other devices OV5640, OV5645, OV5648, OV5658, OV5670, OV5680, OV5693 all of which are 5 MPixel sensors with pixel dimensions both same size (1.4 um), smaller (1.12 um) and larger (1.75 um) than the current RPi sensor.
If it was me doing the work, I'd choose another 1.4 um pixel 5 Mpix sensor in the same family, to preserve best compatibility and reuse of existing configurations.
If it was me voting and someone else doing the work, I'd prefer bigger pixels for better light sensitivity, over increased resolution. However no doubt that costs more, involves more work and I'm 0.0000000001% of the market so I don't think I get a vote
For that matter, Omnivision is not the only company that makes MIPI CSI-2 interface imaging sensors. There is also for example Aptina (now On Semi). In some cases they even put their full datasheets online, how shocking is that... http://www.onsemi.com/pub_link/Collater ... 30CM-D.PDF
The RPi camera market is apparently large enough that there are third-party solutions for compatible M12 and CS-mount boards (Amazon, ebay etc). I don't expect that will change. I'm not criticizing the RPi folks for not providing such options as I doubt the foreign sources are burdened by much CE/FCC testing etc.