It's absolutely not that- it's an early implementation of a drafted WHATWG standard in the "iteration" phase, put behind a development build and a development flag so people know that it isn't stable and might change and nobody who doesn't explicitly opt in will be affected. This is literally made to allow "people who try to set some standards" to test their proposed standards and iterate on them before finalizing the proposal.

As far as accessibility, the native browser select is almost always going to be more accessible than someone making a custom input using JavaScript so they can add some styling control. Having the native version support basic styling is a big accessibility win IMO, because it disincentives developers from making a less accessible alternative for the sake of matching some design file.