Interesting. TP knows this. They talked about this on WDW Today some time ago but can't remember the details just the gist. It's some low number.
Thinking that if every park goer was a Liner, it would prob be ideal. Ha, not only for TP's bottom like but also for us. In an ideal World (I'm guessing), TP would know exactly how many people are in the park (their crowd cals and therefore forecasts would be spot on) and where they'd like to visit (via their plans) and people would within reason follow those plans. Obviously this will NEVER happen. But, in theory, this would allow for extremely efficient plans. Again, just guessing.
Anyway, my understanding is that the number of people using TP really doesn't matter. Our plans react to crowd conditions and optimize accordingly. At least that's my understanding. @Lentesta has heard this question before I know.