I sincerely doubt that anything like this can be removed after being added and after pages start using it...
For typical web features this is certainly true. I feel that this case may be an exception because of the way it's been implemented as an extension.
You have the query the extension explicitly from a function that is documented to return null if the requested feature is not supported.
That function WILL return null on all browser currently, including Chrome.
It's a good bet that it will continue to return null for a decent number of users for a while, even if everyone jumped on the bandwagon today, simply because these things take time to propagate.
It would be ludicrously bad for an app to query the extension and start using it without checking to ensure the extension was returned first. Such a usage is clearly a violation of the most fundamental principles of good OpenGL/WebGL practices, and it's doubtful that anybody caught doing so will have the technical competency to build something of much merit.