Feature size prevents computation from being fast, even if you could tweak it to create "organs" that did distributed processing. Basic limits of what cells can do would constrain the clock speed of any particular compute component to ~6khz or less, or about 100x what they can do naturally.

A mycelial mat, coupled to a PCB, with a few genetic tweaks, though, could allow traditional computers to make use of incredible networks that have trillions of intersections; if you could somehow elicit the algorithm underlying human cortical networks, edit fungi to mirror that, you could get a potent AI hybrid device, about the size of a doormat, as thick as a paperback book, but it's not something where a little chip sized chunk of fungi is going to be useful for a wearable. You might do interesting things with robot sensors, if the electrical signaling translates to touch, maybe a thin network of mycelium over a robot could act as robot skin/touch/pressure sensors?

Bravo, science, fun stuff. We're going to get autonomous cyber hybrid mushroom robots, like a "Last of Us" and "Terminator" hybrid.

That's all fine and good but it would be nice even if we just replaced the plastics used in PCBs with something that can biodegrade and/or renders itself harmless after going into the waste. Truly biodegradable electronics would be ideal but even minor improvements would make a big difference based on the sheer amount of electronics that get manufactured and distributed across the world every day.

I remember reading about using magnesium instead of copper in PCBs a while back. I wonder what happened to that? Magnesium tracks on a fungus-based substrate would be fantastic (and neat!).