NONE of the modifications are based on flashing a Quadro BIOS onto the card. I did limited testing on this (Q2000 BIOS on a GTS450), and all that achieves is lower the clock speeds on the GTS450 down to what they are on Q2000. There is still some stuff in my TODO queue to investigate things like ECC support, though.
To do it properly, you should really change at least a few more things in a addition to the straps, e.g. the record in the BIOS containing the PCI ID (at around position 0x18E on 4xx cards), as well as the board/card identification strings.
FLR is nowhere nearly as required as people indicate. If you pass the whole device (i.e. VGA + HDMI audio) it works fine, and with Quadro (real one or a modified GeForce) rebooting VMs works just fine, if your motherboard BIOS and PCIe bridges aren't buggy (some careful research there is needed if you're looking to buy a suitable motherboard, otherwise you will spend weeks troubleshooting and writing hypervisor patches, and you're pretty much screwed if you use a closed-source hypervisor).
For the record - I have Quadro 2000, 5000, and 6000 cards (real and faux 2000, modified GeForce 5000 and 6000) and rebooting VMs works fine (most of the time - I have problems due to various hardware/firmware bugs that plague the EVGA SR-2). It is ATI cards that suffer from the rebooting crashes and performance degradation after reboots. No GPUs available today have FLR, including real Quadros or real FirePros. It is not needed if the BIOS and drivers are doing their job.
VGX and the new Xen project that implements something similar exposes a guest VM driver API that offloads the GPU tasks onto a real GPU, shared between multiple VMS. Nothing to do with FLR whatsoever. It is essentially a virtualized GPU driver API designed to allow you to share GPU processing between multiple guests.
FWIW, I have had much better luck with Quadrified Nvidia cards for Xen virtualization than with ATI cards. ATI cards have far too many limitations (only a single DL-DVI port from HD5xxx series onward), don't work properly with multi-monitor spanning in my experience (at least not on IBM T221s), and suffer from the VM reboot bugs in the BIOS and drivers (e.g. if the VM dosn't crash on a reboot, the performance is degraded). Then again, I seem to have just hit a XP Quadro driver bug that breaks DL-DVI from working in a VM (but not on bare metal). So neither are perfect, but Nvidia just seems to suck a lot less than ATI (even though I may just have to resort to using an ATI card for one of my VMs if I can't work around the DL-DVI problem on the GTX680 based K5000/K2).
On a separate note, device reset can actually be implemented in multiple different ways, not only if it has FLR support. For example, Xen also supports a method of using the PCIe power management; putting the card into the powered-down state and bringing it back results in the device being reset (if it implements the PCIe power saving functionality properly).