There's a difference between core and nice to have services (eg, ability to tell you the weather), but I consider light, door, and temperature control to be "core": having a dozen separate points of failure is just bad design. You could consider voice control nice-to-have, but if it works well, I have a feeling it would move to being core. If it doesn't work well enough to be used all the time (and thus irritatingly missed when it's broken), why bother?
I'm aware of Mycroft; anyone have experience with it or alternatives?