I have one suggestion, not sure how hard it would be to do. I would be interested in a free rise setting. So the idea would be that, rather than setting a target temperature and heating / cooling to meet that, you set a max (or a min might be useful in some cases). Then no heating or cooling would be applied unless the temperature approached the set temperature.
So this would allow passive rising of temperature due to fermentation for Saisons and the like. BrewPi would only “step in” if it looked like you would exceed your set parameters.
It would be even better if this could be mixed into a standard profile, so only one step, for example, was a free rise, the rest controlled.
Just a thought!