I’ll never say “don’t try an incredibly ambitious project!” because that’d just make me a hypocrite: however, I will say this:
Depending on what you actually want to do with it… you might now need to. I’ve been spending a good deal of time recently working on a setup with Home Assistant, and I used to have my instance on the same pi as my mirror. I honestly think that given the level of features that you want, you may want to look into just combining some projects with something like that – it’s open source still, but it allows your controls, remote access (provided you set up a reverse proxy or open a port), and a stupidly wide-ranging API. Mine also runs Homekit for interfacing with the family’s iPhones. and a custom Alexa skill that ties anything and everything “smart” together.
What does that have to do with the MagicMirror? Well, I’m working on it. For starters, a lot of control over the mirror itself is provided by the URL scheme setup by Jopyth’s wonderful Remote Control module. Right now I have it set up as a switch in HASS (so I can turn the display on/off easily), but I also can use HASS to send notifications to the mirror, automate hiding/content of various modules, etc! That’s all just with the URLs, not even getting into more advanced stuff – I’m working on a module that allows autodiscovery of a Mirror as an MQTT device. With the touch controls built into a lot of modules, you can already control lots of smart home things, and given the expensive API, I’m SURE that you or someone else could write a great module to control HASS directly. Even with what’s available now, it should be pretty straightforward to use the rEST API module to tell HASS (or openHAB, or Domoticz!) to toggle lights, set scenes, activate scripts, etc.
The nice thing about HASS is that it’s written in python and is pretty easily extensible! The bad thing is that it’s configured via YAML. There’s a learning curve, and it takes some tinkering – but then, if you’re gonna try and build an OS, I figure you’re already ready for that.