What you want, then, is more akin to a sandwich press rather than a toaster. Or perhaps a toaster oven. Mechanically, it's not impossible, but the design of a toaster (spring loaded release, heating elements on either side) can't be altered much without turning it into one of those two things (or a poor imitation of them).
Seems a tortured equation: perhaps a vertical sandwich press without the press! I was thinking it may be possible to change the spring to another form of vertical linear actuator (eg. stepper motor driven) and giving it more controlled movement, also smarter with proximity/LOS-style sensors. Perhaps the top cover could also expand and contract. The very fact there's a spring-loaded release shows this is old tech. The market can clearly tolerate a few dollars for a stepper motor, as there are 'smart' toasters selling for nearly ~$200USD and the bottom is ~undifferentiated. See http://www.brevillegroup.com.au/wp-content/uploads/2016/10/B...
Would an ordinary stepper motor cope with the temperatures? Our cheap toaster has a handle that lifts (so isn't limited by spring return); and the socket off switch is the backup for when you need to jam a form in to reach to get your crumpet out.
