We can get to working semiconductors in our garages relatively easily. They won't be anything like the integrated circuits we have today.
It would be an interesting hard sci-fi novel to see the village black smith replaced by the village semi-smith and wind mill replaced by the nuclear mill.
Lithium batteries will be dead within a decade. Solar panels within 3. Think about that the next time you cheer on a huge solar installation as a win for the planet.
You can get away with having a single global state variable so long as it's an association table and you keep track of what variables you've introduced. I believe that the reason why people thought it would be slow then was that no one had used a data structure that could store multiple results for the same value.