Artillery Games is taking it beyond a demo. They are developing a fully 3D Real Time Strategy (RTS) title, trailer above, based upon these web standards. The team of 11, 12 including the company pet, consists of many ex-Googlers along with alum from Intel, Lucasarts, Adobe, and more. Their video is quite impressive and, I would say, comparable to an XCOM: Enemy Unknown or StarCraft II level of graphical quality.
That is pretty good, considering we are comparing the Real Time Strategy to full RTS releases.
Being compatible with web browsers also affords quick turnaround for developers. Changes will not require a lengthy compile process as web standards are compiled at run-time anyway. Modifications should require, at worst, a browser refresh and, at best, swap by the next animation frame. This level of rapid iteration should help developers polish their creations quickly.
Speaking of quick, a private beta is expected before the end of the year. Full release is scheduled for some time in 2014. Their demo is shown on Firefox and Google Chrome. They have not mentioned anything about Internet Explorer 11, the first IE release with WebGL support, but who knows.