Yes, hence why I commented that MS never prohibits you from publishing your extension elsewhere. Nor does MS forbid you from using other marketplaces when using their product. It's like saying valve is prohibiting game dev from publishing their game elsewhere or distributing their game outside of steam. It's just not true. And MS has all the right to limit their marketplace to their own client too. After all, it is first and foremost, their service for their product specifically. It's like you're making an unofficial client for youtube.