BeOS was mostly a single-user system, and filesystem was optimized for that use case. Having to consider that an opened file for reading may be modified by a remote system running with a different user complicates things, so while I do agree that BeFS was quite ahead of his time, it focused on a somewhat specific use case; At the time, you wouldn't expect that you could eg. correctly backup your email client data without shutting down the application.

> it was just a SQL database that stored arbitrary data.

I mean, for some definitions of “just”, “SQL database”, and “arbitrary data.” :) It was a schematised graph database implemented on top of a slimmed-down version of SQL Server. The query language was not SQL-based.

> It was abandoned due to The Cloud.

It was discontinued circa 2007. The cloud was much less of a Thing back then. I don’t recall that factoring at all into the decision to cancel the project, though it would have been prescient.

(Disclaimer: I was on the WinFS team at Microsoft.)