Just don't use any plastic parts, over-engineer the whole thing internally, no wifi, just a dial for temp and lever to engage. All these fancy toasters still can't toast bread.
I would imagine the percent of people who are looking to buy an expensive toaster is small, the percentage of those customers who know how to code is even smaller, and the percentage of those programmer customers who have time to and are also interested in programming their toaster is vanishingly small.
You might be right but I highly believe that it would increase in popularity once you have more local only devices in this space.
I have plenty smart devices with stupid apps, but I would pay premium for a quality product with a simple API and no third party servers anytime.
Personally I base many buying decisions around 'hackability'
Edit:// actually I think this is a coming market as Google only recently started to support smart devices without third party servers for their home app so before that local only ment no Google home most of the time.
Smart timer, finish notifications and statistics. Nothing would make my breakfast better, but I surely cannot be the only one who would pay more for a device like that. Maybe I am..