IIRC, the first model ate mosfets for breakfast because the photo resistor is way too slow going from illuminated to dark. That leaves the mosfet in a fairly high resistance state for an extended amount of time during which it dissipates a lot of power. You should add some kind of Schmitt trigger inverter that buffers the resistive divider and gives you a clean narrow edge to drive the mosfet gate. A 74HC14 together with a 7805 voltage regulator should give you enough output voltage to drive the mosfet. These chips cost less than a single replacement mosfet and you can drive 6 coils with them.

I hope they will. My guess is that a nonprofit like Signal will pull out. They have nothing to gain and a reputation to lose. The others will probably comply by implementing some form of client-side scanning.

If they force messengers to implement backdoors into the protocol, I doubt they will limit it to UK users. Also, conversations with UK users won’t be private anymore even if the other party is from another country.

Client-side scanning might not be enforced for other accounts but when the infrastructure is there other governments will want to use it, too.