Plus its a regular problem ensuring that an API is stable. People do it all the time - aren't you wondering why you are the only person arguing this point? Many people in this thread deal with these problems on a daily basis...
Your software can’t be updated. You have one try to do it right.
It’s what next to all of the modern startups don’t get right. They build fancy software, but then in a few years your smart house doesn’t work anymore because the services it connected to have changed APIs and the house itself encountered a few bugs?
The lifetime for a washing machine is 30 years. Your software on that will last 30 years. Using a development method designed to make quickly changing requirements easy is stupid when your code will be "write once, never change".
Same with stoves or fridges.
We already see how hard it is to keep mobile devices updated. Android is the nightmare example, but even Apple drops devices after 4 years. In 20 years, your smart fridge will have tons of malware on it if it’s connected to the internet. If it isn’t connected, you won’t be able to get updates, so the software has to be perfect.
And the point we made in Uni was that agile is suited for situations where your requirements change after deploying. In all other cases you can do waterfall – provided you actually find out what you’re supposed to do – better.
Personally, I want my appliances 100% electromechanical. I don't really get the whole IoT buzz. Besides simple reliability and repairability, I have no desire to control my stove or washing machine with my phone. I can get up and punch a button.
Warning: Expensive. Really expensive. Their washing machines start at 1300 USD.