I've been thinking the same thing! The app should have protocol templates for whatever intervention I'm testing, what outcomes I should track, and what confounds might be. And if it isn't part of the templates, help me develop the protocol, including being able to set what level of confidence I want. It should tell me what actions I should take to improve confidence (e.g. bloodwork). It should hide the results from me until the overall intervention is complete.

All the other health apps and tracking systems I've seen are operating at one level of abstraction too low (just the data itself and its direct insights), or try to find patterns from p-hacking passive signals (it looks like when you work out you sleep better, did you know your HRV is 1.1 higher when you do [unrelated thing]). There's no buy-in or sense of direction in these products, no pushing me to do more to acquire data, no laser focus on a targeted test / intervention.