The Synergy lineup is already really solid. Anything new would just be a slight variation on something that already exists. I understand they need to keep releasing new products to stay relevant, but I don't see what releasing a Recto or 5150 is going to give if you already have the Uber and SLO.
I guess Orange could be interesting if you're wanting something more doom oriented, but any of their more modern amps, like the Rockerverb and Terrors, could easily be replicated with an 800 or Friedman module. Wizard and Larry are never going to release a $400 module when their amps cost 10x that. Aren't they just high end modded Marshalls, anyway? Plenty of that in the Synergy system already. Driftwood, Mezzabarba, KSR, etc are all covered close enough by the Uber and SLO, too.