This seriously disturbs me. Dropbox has several fundamental flaws that make it entirely unsuitable for widespread adoption as anything other than a personal file store for people who don't care about privacy. A "filesystem of the web" would need security, encryption, fine-grained sharing controls, reliability, and numerous other features. Meanwhile, the whole sync mechanism of Dropbox doesn't really matter for a "filesystem of the web", because changes can just occur directly in the remote filesystem rather than locally with syncing.
Now, if someone called S3 "the new filesystem of the web", that would make more sense. Numerous services build on S3, including Dropbox itself, and it provides enough tools and API to allow those services to include all the critical features mentioned above. Add a few features for users to hook up their own S3 data to services rather than the S3 accounts of those services, and you'd have something even more interesting. (The same thing applies to any equivalent service to S3, and many such services exist.)
Meanwhile, the whole sync mechanism of Dropbox doesn't really matter for a "filesystem of the web", because changes can just occur directly in the remote filesystem rather than locally with syncing
Excel can't make changes directly to the remote filesystem. That's the novelty of this scheme. It isn't yet another cloud database, it's a way to share local files with cloud apps.
I have mixed feelings about this.
It could serve to bring data out of the silos, and back under user control. That would be an epic win.
But it's not federated. And I anticipate problems with access control, which needs to be per app, per file, and separate read/write.
Aside: I recently had a nasty scare when a shitty iOS password manager deleted my Keepass database from my Dropbox. If hadn't found a copy in the Dropbox cache on my laptop, I would have been in a world of shit.
I'm writing this reply from a commuter train with wifi that goes away whenever we enter a tunnel. My point of view is that a filesystem of the web has to support disconnected operation. The Coda filesystem has worked that way for decades.
Now, if someone called S3 "the new filesystem of the web", that would make more sense. Numerous services build on S3, including Dropbox itself, and it provides enough tools and API to allow those services to include all the critical features mentioned above. Add a few features for users to hook up their own S3 data to services rather than the S3 accounts of those services, and you'd have something even more interesting. (The same thing applies to any equivalent service to S3, and many such services exist.)