That's a great point! I am actually working on it One of the first tests will be to look at the correlations between the sleep quality/Deep+REM sleep and reaction time and focus. These have been shown to be correlated by sleep researchers. What I have for now was not enough to produce statistically significant correlations (I had about 25 nights of data, and used Spearman's rho for robustness). I will be more than happy to share data with you, if you are interested.
I can say for sure that so far Quantified Mind is the best platform for self-assessing cognitive states. The mobile version could be a great way to monetize it.
I also was going to ask you about batches of tests available on Quantified Mind (e.g., circadian rhythms). Is there any kind of guide or some intro that could provide more explanation on which test to use, and how they were put together?