I am hoping that the idea of putting all the eggs in one basket with dilithium as a warp source and power modulator will be explored.Putting all your eggs in one basket is never a good idea. If something happens to Stamets, they can't use the Spore Drive. Book still knows more about the galaxy than Discovery (or Starfleet for that matter). Being a guide and negotiator will probably be his main function. He's like a much cooler version of Neelix. And he can help with the Spore Drive as an added bonus. But that won't be his main thing.