Since the release of 3.1 back in December 2015 there have been many great bug fixes pushed to master. For example, on OS X, there was a nasty bug where 100s after opening a VideoCapture device, openCV crashed. It has been patched in both OpenCV master; and we have a patch (to apply to OpenCV 3.1 source release) in the conda-forge feedstock (that we use to distribute it and the Python bindings). There a quite a few other patches that are queueing up for conda-forge to include, and it might be nice (unless 3.2 is soon) to make a release to help down-stream distributions from having to maintain a patch list.
Example bug: https://github.com/opencv/opencv/issues/5874
Discussion: https://github.com/conda-forge/opencv-feedstock/pull/29