Yes, the issue I was having with the tributary CB is that -- even though it was reduced to an ai_will_do of 0.01 -- often that was the only CB that would be available on a target, and thus the AI would employ it constantly. So currently the AI is restricted to only have it available to non-nomads when the realm is emperor-tier or when the realm is quite large (100+ realm size) and the ruler is ambitious/greedy.
If there are other criteria to apply, I could open up the restriction some more, but my impression has been that it's not really a useful CB...and that the AI will often screw itself by making tributaries out of lands it really should be conquering. If there are specific conditions under which that isn't the case, conditions I can teach the AI, I'm willing to do it, but not if it results in the situation once again where there are nonsensical tributes everywhere.