Why not a box with a special OS (ala WAFL) that runs on what servers recognize as a fibre hub, intercepts the SCSI calls from all attached servers, and does all the nifty stuff needed to make the SAN(?) look like locally attached storage? Advantage? Separate file I/O from TCP session traffic but still allow file sharing in some form or another.
SCSI is a raw disk block protocol. SCSI requests are very simple. They say things like "read block twelve-million and two" from disk, or "write block so-and-so to disk." There is no way in SCSI to express file level ideas like "create a file named foo" or "read the first block in a file name bar".
If you make the data look like locally attached storage, then all the different hosts will access it using their own local filesystems, so the different hosts will each use a different format, and the data on disk cannot be shared.
If you want the data to be shared, then you have to find some industry standard filesystem sharing techniques that everyone has implemented. Today the only such standards are the NAS standards (like NFS, HTTP, Windows Networking).
There are a variety of theoretically possible solutions that we could develop, possibly involving new file sharing protocols that could run over SCSI, or "global file systems" that everyone agrees to run on their system. But there are lots of tricky issues to resolve, and the standards work has barely begun, so even in the best possible case, it'd be many years before we could get a true heterogeneous data sharing solution.
Dave