I've read about this and I'm a bit confused: java applets have always been able to use OpenGL, so these security concerns should be nothing new. If they're an issue, they should always have been an issue with Java applets, but nobody seems to have minded until now. Microsoft have been under pressure to implement WebGL, and they seem to have highlighted these concerns as reasons to not implement WebGL, when I guess the real reason is they don't want to support anything OpenGL related. This is frustrating, because obviously WebGL support would be great for Construct 2 - the exporter could match Classic's features, shaders and all, in a browser.
Google have been working on JebGL (http://code.google.com/p/jebgl/
) to bring WebGL support to Internet Explorer via a Java applet. We could use that, but then it defeats the whole point of having a plugin-free system. A quick Google showed that Java support is on about three-quarters of machines on the internet, so support is still OK. Surely there are going to be some compatibility issues though.
It's still very early days so obviously we're still going to stick to good ol' canvas (which IE9 does very well), but in future we might develop a WebGL/JebGL exporter more as an experiment than part of the product, just to see how it works. For 2D games, WebGL doesn't add much more than just eye candy, and given the support isn't so good, it doesn't seem worth it right now.