A complete set of multi-effects for each of the 16 parts. No more of this "x" number of insert effects (3, 5, or 8, or whatever).
I want single voices/programs to sound exactly the same in song mode as they do in single mode. And I want 16 of them at once.
You just described the Roland Integra 7. Granted it's not a "workstation", but It does exactly what you've described.