I do believe that this thread: Revamping Compound Clouds
Held the majority of discussions related to passive absorption, though its focus extended to a complete refactoring of how we dealt with compounds as a whole. What was generally settled out of this discussion was that phosphate/ammonia would be dealt with passively, but having every compound be dealt with passively would seriously take away from active gameplay in the cellular stage. Cellular interactions likely won’t be complex enough to have our active gameplay completely foresaw actively pursuing clouds.
Nonetheless, good ideas to bring up with phosphate/ammonia environmental concentrations being influential on absorption rate, and membranes. Right now phosphate and ammonia are obviously flat across environments, but when we eventually want to slightly reduce and vary their availability, that could be a strong incentive for becoming heterotrophic.