[1]https://m.youtube.com/watch?v=Y_lqIUlON1s (5.38mins)
The results appear to be fantastic at preventing colony collapse disorder. And the hypothesis for why it works is just complex enough to make sense in an ecosystem: varroa mites aren’t directly killing bees, but due to pesticide use the bees are more vulnerable to the viruses/infections that the parasitic mites carry. Bees seek out certain fungus mycelium to lick in order to get access to their antiviral and antibacterial properties. Stamets’ solution (literally) is to put a small amount of those harvested chemicals into the sugar water that beekeepers feed their hives.
As for practicality, growing mushrooms is very very easy to do at scale for many known species, IIRC this includes most if not all of the species Stamets has found to be beneficial.
My only qualm is that it cannot address the threat of extinction to our US native and solitary bee species. So I think it could be a necessary but not sufficient step if keeping native pollinators extant is a goal.