Personally, what I'd like to see is Synergy release some original/exclusive modules. It's great that the amp builders are the ones who designed their respective modules. They sound awesome, but it's also still trying to capture a flagship amp in modular form which can only take you so far.
Synergy already has the basics covered. How about something designed from the ground up that's unique and NOT trying to capture an amp already in existence. Imagine if they released a fresh
Engl, Friedman, Soldano, et. all module that was unique to the Synergy system.
As far as other hardware a 4 slot preamp (SYN4) or a 100 watt head with 3 slots + dedicated clean would be really nice.