I don't know, the last line is pretty critical. "But the trade-off is giving more power over your life to a company that probably already has too much."
It's harder than a walled garden you control but very feasible.
Heck most software engineers could put together a smart lock and app to do this in a couple of months. Wouldn't be consumer ready by any means but this isn't some huge engineering challenge.
Figuring out how to market the product successfully is the harder part.
And exactly this is what limits it to "a large/powerful company".