First, just to address one technical point - if we're assuming a networked environment I believe any number of (properly tuned) client-server DBMSs will outperform VFP, because bandwidth between the DBMS process and the local hardware is higher than any 100Mbit (or probably even 1000Mbit) network connection would be. On a single workstation/local machine VFP might be hard to beat, I don't know, but there are some lightweight, highly tunable/configurable products out there that can yield high performance (FairCom, Raima, etc.)

Second, I get the feeling you've got a bit of a bee under your bonnet on this topic, since George Tasker (to name one person) has dismissed your conclusions. However, it's a long way to go from, "fragmentation seems to help in some tests I've done in VFP" to "fragmentation helps most applications most of the time". You'll need to do a (hell of a) lot of testing to establish that - testing that will need to be consistent and repeatable (i.e. the scientific method ;-)) Put some real numbers to your assertions.

If you don't think developing a fragmenting algorithm would be hard, then try it. The first step would be to write a hard disk emulator and then simulate read/write operations to it.

Finally, it's worth pointing out that for some time, Windows has supported 3rd-party installable file systems. No-one's forcing you to use NTFS, or preventing you from writing a file system of your own. Have at it! ;-)