I guess you mean this thread: Expression Maps for Dorico 3.5+ - Dorico - Steinberg Forums
Unfortunately, NI symphony series is not mentioned.
Yes, NI symphony series only providing 8 slots for keyswitches would be a problem. Still, I would very much more like to adapt an existing XP map instead of starting from scratch. I have never created one, as I am very new to Dorico, so maybe I over-estimate the effort to create an expression map. But usually these things take longer, not shorter, that you would expect.