Can you elaborate on the current state of IE11 support? Unity WebGL gives a "not supported" message when loading content. Do you know what currently is/is not supported?
There are probably other things, by primarily WebAudio is not supported. Firefox is really the only supported browser at the moment.
You're right about WebAudio on IE although it seems to work other than that. Chrome also seems to run well.
Yes, Web Audio is not supported in current IE, which is the main reason we don't officially support IE yet. The other is that current IE is rather slow when it comes to executing JavaScript. Luckily, MS is adding Web Audio support, and they are working on an asm.js JS engine, which I expect to get roughly equal performance as Firefox. So I believe that IE will actually become one of the best browsers to run Unity WebGL content in in the future.
Technically it probably wont be IE but rather Microsoft's replacement browser unless they plan to keep updating IE for awhile as well.