Check their original Substrate talk at SIGGRAPH from 2023- advances in real-time rendering. They do want to get to phenomena like florescence, but I don’t think it’s a major priority atm because they listed bigger priorities like making it more performant.
I for one will absolutely love to watch substrate get built out to handle the next-gen of material rendering, but considering how even one complex substrate material can easily be too much for a scene’s performance, I think speed is a priority.