It is a great option to access IPFS via WebDav. Seems like it is quite easy to make it possible to open IPFS folders. But it can’t be writable, because webdav URL should change on every write operation. Writable mode could be suitable with IPNS only.
Webdav have LOCK operation, file meta. This part is going to be broken, difficult to implement with IPFS.
Even though, it is a great idea to use very common protocol to access files.