Like other commentors, my immediate use case would be to sync Joplin note databases, but there are half a dozen other applications that could allow me to do away with Apple, Google, and Microsoft cloud services. Can't wait for the day.

This would allow me to use the terrabytes I have on here for a lot of purposes, freely : Proton would become the center of everything I do that need storage;

Webdav would facilitate connecting ProtonDrive to OnlyOffice. This would be a big step towards replacing the entire Google Docs suite. I vote this as a priority feature.

As others below, I arrived here after searching for webdav support for Proton Drive so I can sync Joplin. Currently using OneDrive, which I'd love to ditch.

No idea how webdav works, but I believe that it s needed for Joplin to work with Proton Drive. Therefore I am all for it (just as long as security does not get compromised for convenience).

Love to have WebDAV for Joplin

This would help immensely with migration to Proton Drive!

I was just about to pull the trigger on an Unlimited plan assuming Proton Drive had WebDAV capability, because I'm tired of doing the maintenance on my self-hosted Nextcloud server. Glad I checked. Might have to suck it up and keep using NC until this is added.

A must have to Sync folders of my Asustor NAS. Please, implement.

I currently need to use the Onyx Boox drive for cloud storage -- would definitely prefer to use the Proton account that I trust.

Webdav would be very appreciated
But then it should be possible to create app-specific credentials and restrictions to dedicated folders for webdav

Lack of support for open standarts, such as WebDav, CalDav are showstoppers. They are more important than any UI feature. Using a WebDav would allow connecting office suites, such as OnlyOffice and synchronize calendars in Thunderbird. Proton is targeting power user and support for open and secure access protocols is key missing feature. Many such users are working in Linux desktop where Proton drive is not even available, so WebDav and CalDav is the only way to get access to data.

As noted in other comments, any open standard is good. Anything you can already mount on Linux, presumably via a bridge.

proton-drive is pretty much useless without a programmatic way of moving data to it from Linux and Truenas. Rsync or ssh or webdav please. As others have said, moving files by hand through a web browser is a shitty way to do backups. Especially with all the warning dialogs about 'files too large' and 'don't stream at the same time'.
This can be done in a roundabout way with the windows proton drive app running in a vm via a shared folder with the linux host but I don't trust microsoft enough for that kludgy method.

Will upgrade from free to ultimate when webdav is implemented. Now using strato hidrive with webdav

Any comment, when you will implement WebDAV?

Absoltue must. Same reasons as people stated here before me.

Need WEBDAV for Sync and as TeamDrive-Server (Storage). I have a paid plan for proton products.

I need to automate backups to proton drive to make it useful. From truenas or synology nas. Webdav would work. So would rsync. Having to upload files one at a time using a browser interface is a horrible way to do things.
Both Synology nas and Truenas support multiple cloud storage vendors but proton drive is not among them because of this missing feature. I am keeping a paid proton plan and praying for this problem to be fixed.

As long as Webdav is not possible I will continue to use free versions of Proton. If Webdav is possible I will become a paid user for Mail, VPN and Drive. This way I stop with services at other providers.