But if you look at devices with cycles in between, I already see it happening. 10 years ago when I bought a stereo receiver, I bought something entirely dumb. Last year I replaced it and ended up with something that was internet connected. Not because I really cared, but because the equivalent model came with that. And in retrospect I'm glad; their phone/tablet app is a way better remote control than punching a bunch of mysterious, no-feedback buttons. The same thing happened with my DVD player; when the old one died I just bought whatever Consumer Reports recommended and it too is internet connected.
I think that you're right that the development of pluggable Android is what will push this forward. And Google clearly agrees; their project Brillo is surely one effort among many.
I've always thought that the reason for keeping Android as open source was to enable this use case. Eventually, Android-capable SOCs will come down to a very low price point, and for these use cases they don't need to push much more than a few kb per second. But it retains the advantage of having a development ecosystem that is well understood and widely available (you can't throw a rock in China or India without hitting an Android developer).
The situation with your daylight system is a perfect example. People think "Oh, that's cool" but won't actually get off their ass and spend a few hours setting it up and configuring it to their liking. Unless it comes out of the box, it's a non-starter.
IoT devices as they are today require a systems integrator to come in and tie everything together and configure them. So your lighting system is integrated with a presence system that is also integrated with your thermostat. Each of these has to be configured on a case-by-case basis, because no two homes are alike. But if your products require an integrator, suddenly the integrator is your customer, and you begin sacrificing end-user focus for things that make the integrator's job easier.
And then you realize that the largest consumer of IoT platforms isn't consumers themselves, it's installers like ADT. Their focus is on selling simple products that require minimal support, not feature-rich ones. Why? Because users simply aren't interested in paying any amount of money for advanced features. Until that changes, IoT is going to be a niche hobbyist market. Even if it's built in to every device you buy, if it's not worth anything to you, you're not going to configure it in the first place.