This already exists – it’s how I do things. My Nextcloud file system is mounted as part of my regular file system, and my obsidian vault is in that file system, so it gets synced everywhere along with everything else I have in Nextcloud. I’m running Nextcloud on a Digital Ocean server and it syncs everything between my laptop, phone, iPad, etc. Nextcloud is integrated into the iOS files app, so I can view Obsidian files there (and also in apps that fully support the files app – but here you’ll find some inconsistencies).