In addition, the safety aspect of this could be a big advantage. If you get it UL certified etc., then it could be marketed as a fire prevention feature. A $10 toaster can cause a $100,000 fire without even drawing enough amps to pop a breaker. If you get some insurance company to give a discount on fire insurance for using one of these, and the product could pay for itself.
Just some thoughts, best of luck!
I've also worked in several workplaces that ban toasters in staff kitchens due to the cost of false fire alarms. Someone always burns the toast.
From [1]:
> An ICSD smoke detector is composed of a housing made of polyvinylchloride or poly-styrene plastic, a small electronic alarm horn, a printed circuit board with an assortment of electronic components, and a sensing chamber and reference chamber, each containing a pair of electrodes and the radioactive source material.
[1] http://www.madehow.com/Volume-2/Smoke-Detector.html#:~:text=....
If you're going to automate toaster shutoff as you suggest, maybe do it when the toast is nicely done instead of waiting until it's almost on fire? Just a thought.
Adding a smoke detector is more for safety than to get the right toasting level, although personally I like my toast well done, which is just when the first wisp of smoke appears.