Then you'll get local shops that sell the machines painted in 2-3 layers of faraday paint (or apply some sort of cage, or solder out the antenna, etc). Or perhaps just like in the old console hardmod days everyone will know someone that can "mod" your dryer so it stops being dumb and just dries your clothes.
BTW does anybody know of any pointers to community projects that are making hardware for this type of thing? I've got it on my long term todo list to create a replacement board for a washer with a "bad control board", but wouldn't want to waste the effort if there are already projects doing this.
I could imagine a little microcontroller and say 10 relays that can control the pump, motor, valves, etc. Then you sell it together with instructions which specify how to program in which output does which function.
You could sell it to people who want to "IoT" their machines for cheap, to people who have a dead control board, and people who want to customize their appliances (eg. I need a custom wash cycle for washing extra dirty clothes).
I don't know if you'd even 10 relays. Most appliances have been cost-reduced into like two motors, a heater, and one or two actuators. Perhaps newer models with steam cleaning etc have reversed that trend.
Control side, I'm thinking of an AVR + ESP32. The AVR for reliably controlling the motors with the sensors, eg if the water is full, turn the water off. True safety stuff like overheat switches obviously stays inline though.
One of the more complex details is newer appliances have moved to brushless motors for efficiency. A three phase motor driver is straightforward, but figuring out what design parameters will be reasonably generic to serve the most appliances is some research.
The least generic parts seem to be fitting in with the existing user-input buttons, and managing the complexity of programming many different models for non-engineer users. The kind of people that are comfortable taking apart appliances generally have less patience for programming computers.
Of course if any specific model became popular enough someone could fab a dedicated control board that fit in the right spot, or at least had matching aesthetics.
I would just snip off the antenna or remove the SIM, but if I can think of that, so can the manufacturers.
My sim "card" today is just an email already.