Glad to see so much excitement about Fabrice's P600fw upgrade. Despite having lived and breathed Prophet 600 firmware and hardware for nearly 6 months, I've only thus far tested Fabrice's alpha release back in February. From reports here, the beta release sounds quit amazing.
A couple of things to mention: yes, the Teensy++ modification is a little fiddly and if you don't have much soldering experience it could be a daunting installation. There isn't much risk to your Prophet as you're just swapping out the CPU, but even I didn't get it to work the first try.
It should be fairly trivial to design an adapter PCB to make the P600fw Teensy upgrade more plug-and-play compatible (ie. no modification of the Teensy++, but it would still require having the firmware loaded on to it for the first time). I've toyed with the idea. If no one else is doing it and there's enough interested I might give it a go (and make it open hardware, of course).
Fabrice's firmware is OPEN SOURCE. If you are so inclined, you can download and modify the source. Want MIDI sync'd seq/arp/lfos? Hopefully Fabrice will give them to us, but even if he doesn't somebody will eventually. Fabrice has open sourced the entire firmware architecture of an early 80s polysynth. The hardware architectures of the early 80s analogue polys have a lot in common. I predict that this project will become a great learning resource for people wanting to try similar things with other polysynths (although the list of synths needing upgrades grows shorter every year) and even for the ambitious among us that might want to have a go at a completely DIY polysynth!