I’m not sure you need to sell it to actual users. A lot of benefits of an advanced filesystem could be done by the OS itself, almost transparently. All of the features I mentioned could be managed by Windows, with only minimal changes to the UI. Even reflink copies could just be a control panel option then used by default in Explorer (equivalent of cp --reflink=auto in Linux). And from the OS side, deduplication would help a lot on Windows given all of the DLL bundling, and weird shit they have to do to maintain legacy compatibility, and that’s no small thing given how space inefficient modern Windows installs have become.

It would be some work to upgrade it (maybe a lot given how ancient and likely full of cruft that Windows is full of with legacy compatibility) but it would eventually make the system more reliable and more space efficient.

But yeah, there are challenges. I’m mainly speaking in terms of btrfs which would take some time to port to Windows (although there is a 3rd party driver they’d want to handle it themselves I suspect) but they’ll probably want to use their own ReFS and I’ve not really investigated it seriously so I can’t say how ready that is for prime time. But given that it’s being included as an option in some enterprise/server editions of Windows maybe it will be soon in consumer editions soon anyway (as much as I’d prefer something more open and widely supported, at least it’s a step forward on Windows).