The concern is shipping a non-standard solution and then encouraging developers to use it is the first step toward lock-in. No matter how much you flag somethin

The concern is shipping a non-standard solution and then encouraging developers to use it is the first step toward lock-in. No matter how much you flag something as experimental, it will be used, and the developers who built things using it will move on. When other browsers later implement the standard, nobody goes back to build it in to their projects- they're working on new projects now. This is how Firefox can support Web Audio and still not have it work on the majority of sites that use it. A differing implementation is just as bad as a prefix, and hurtful to future developers who will have to code for it to reach a compatibility matrix.