Like a kill to death ratio in Call Of Duty!
I like this suggestion. One of the thing that love about Zwift is the idea that each individual might measure “success” or set goals differently and Zwift supports all these different mechanisms.
I’m a little left-brain and like the idea of, for example, saying I am going to do a ride that gives me a net gain (overtaken - passed) of 20. That adds a little variety to the workout too, since it’s only after riding for a while that I’d have a sense of how long the 20 might take - or even whether it’s feasible 
So, yeah - love this idea. Just need a “net gain”-type indicator somewhere in the dashboard (configurable to be visible, since I’d guess that a lot of people would find it uninteresting).
I work with a guy named Scott Bryan. And shot him up in Call of Duty too a few times.