Except that you couldn't actually pull this off unless you were a large/powerful company.
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".