Supported is probably the wrong term. Tolerated might be better. Whilst Windows runs on it theres very little there beyond the usual Microsoft standard of "yep we did it, whats next" and ignoring the platform.
Making it work on ARM is one thing, making it work well, and supporting the platform are a far more important part of the puzzle.
Making it work on ARM is one thing, making it work well, and supporting the platform are a far more important part of the puzzle.