I get what you’re wanting to do. Instead of exposing hubs and bridges to Homebridge in order to control them, you want to expose HomeKit to a hub for controlling it. I can see Apple continuing to allow Homebridge with no legal action, becuase it requires iOS devices and an Apple TV to do automations, and most people will not use this web UI for configuration, they’ll still use an iOS device. Plus you still need an Apple TV 4 for automations. What I cannot see is them sitting idly by and allowing the reverse to happen. So the next best thing would be a new version of homebridge that allowed automation of devices, without duplicating Apple’s interface. Since we don’t have that, just buying an Apple TV 4 and using an iOS device to create the automations is the next best thing. I was able pickup an Apple TV 4 (non-4K) from ebay for $100 CAD. Not that big of an expense considering what I can automate together with it, and all local, plus we’re enjoying the benefits of the newer generation of Apple TV vs our older gen 3.
For me, I was really wanting to bring my Insteon devices under local control by Hubitat, and with this setup, I have it. Doesn’t allow me to dim, but of the Insteon dimmers I have, the only one I ever dim is our deck light on summer nights, and I can just do that at the switch, their app or Alexa. Doesn’t matter to me that I need cloud for that rarely used function. It’s the daily ON/OFF control I don’t want to be dependent on cloud reliability.
I have an Ecobee 3 as well. I may be mistaken, but I believe that no matter what you do, outside of HomeKit, it is still going to need some element of cloud for automation. There is a port of the Ecobee SmartApp and DTH (called app and driver on Hubitat), but it still needs OAuth, and I recall one of the Hubitat team members stating they need cloud for OAuth. So it’s still not pure local. Honestely, I have had so very few incidences I can remember in almost three years of owning an Ecobee 3 that I can recall not being able to access it remotely. Plus, there are advantages to some of the cloud integrations that cannot be done via HomeKit. For example, I don’t have A/C, but I can integrate it with Stringify, so if the temp in any room rises above a specified level in the Summer, the fan will turn on, even though the mode is set to OFF.
Cloud has its place. SmartThings cloud is so unreliable in comparison to other manufacturers, that I get why you’re wanting to run from it. Once you’re enjoyng the stability of Hubitat, you’ll probably feel more comfortable with a balance of cloud and local. I’m really liking the Homebridge and Apple TV combination. Thanks to the work of @pdlovelace and @tonesto7, the Homebridge-Hubitat plugin has allowed me to locally control another hub from Hubitat via the automations, even though there are no direct Hubitat integrations ready, and so far it’s proving to be very fast and stable. In fact, there are so many easy to install, and generally easy to configure Homebridge plugins for devices that don’t already support HomeKit, you can practically automate interactions between any other ioT device and Hubitat.