I'm an old school full amp guy too, and every couple of months I'm still tempted.
I don't look at the Synergy stuff as full amp replacements, but rather as a way to make one rig that truly does everything you'd want for any given live environment or a studio session where you don't want to bring everything you own. Honestly, if I could put together something like two SYN2's with these modules:
Tone King Imperial
JMP
Killer Kali
Vai
...I think that would truly cover pretty much everything. You'd get 8 instantly available tube preamp channels representing basically almost all the major gain levels and textures, each with a full set of physical knobs, all in two rack spaces. Insane.