I think acorns would make a great substrate. Please post your results if you try it. If you smash the kernels they will undoubtedly contaminate. Bacteria will run through the mashed acorn faster than you could imagine.
Mycelium has no trouble at all colonizing wet cellulose. I can bust open a fresh acorn shell with my thumb and forefinger to remove the nut. Mycelium can reduce the hardest woods to pulp that resembles a sponge disintegrating in your hands almost as quickly as it can through
straw.
If a mycelium can colonize a substrate of acorn
wood (oak chips) in 10 days, dont you think it could just as easily colonize the acorns?
I would dry them first, using an
oven or whatever.
My last thought on this is that it will not work if you just pasteurized the kernals any more than pasteurizing wheat berries would work due to the high nutrition content. They would have to be pressure cooked just like grain spawn.