JFYI there have been experiments for that (and the driver actually worked experimentally but then at the time nobody was interested):

http://reboot.pro/index.php?showtopic=7681

and multi-commander has a plugin for this (though this is more like representing the registry as a filesystem):

http://multicommander.com/docs/browse-registry

As I see it the Registry format has many common points/similarities to NTFS, it is somehow a cross between a filesystem and a database or can be "seen" as either.

Previous post/discussion with some more links:

https://news.ycombinator.com/item?id=27940874

you can sort of do it in powershell you can browse it, e.g. ls HKLM:\