Progress on webgl support is flagging on windows. Late 2014 and early 2015 where good times for WebGL overall, reaching new all time highs with currently 86.1%. This is largely thanks to rapidly advancing support in the past months by Internet Explorer, iOS and OSX safari. Even traditional sorrow spots like Android Tablets are showing promising signs to recovery. Inside that progress however the picture is more mixed, windows in particular has a problem across all browser vendors.
On Windows the situation presents itself as follows:
Chrome: A high of 97.1% established in December 2013 has not been surpassed since (currently 92.8%). In particular a local peak of 95.3% in August 2014 (just before a bogus blacklist entry got inadvertently released) has also not been surpassed since. The post recovery curve is now flat since November 2014.
Firefox: A high of 83% established 2014 has not been surpassed since (currently 81.1%). After a rapid dip in september/october/november 2014 it has started to recover, but the curve is now flat again.
Internet Explorer: After a quick start into high levels of WebGL support during October 2013 at 0% to November 2014 at 79.4%, a high was reached in 83.5% in January and has not been surpassed since. The curve for activation has also flattened out since November 2014.
I can only speculate as to the reasons of these developments, but I suspect it would be a combination of these factors:
Internet Explorer is still struggling to expediently replace older versions. Although that situation has improved, the peak to peak distance of IE versions is: 7->8 = 28 months, 8->9 = 18 months, 9->10 = 10 months, 10 -> 11 = 14 months, and so this does contribute to the flagging advance in WebGL support by Internet Explorer.
Driver/Hardware issues are preventing support from closing the remaining gap as well.
At current rates (which might not be indicative to future activation rates), support on Windows for WebGL will not advance beyond 90% in a meaningful way for a very long time. As is usual, the last mile is usually the hardest, and so I'd encourage everyone to look into ways to close that last 10% gap.