[aforwardslash]

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.