You might be able to do this and keep the Elk, but I don't think it will be easy. There is a community effort to do this on SmartThings, and it looks like another user has helped port it to Hubitat. You can find a few more threads here (and there) if you search. None is for the faint of heart, and I'm not sure how functional either is.
If you're OK with replacing the "brains" entirely with Hubitat, you can also look into something like Konnected.io (either the commercial product or building your own with an ESP8266 and the software), but I understand that you were asking to avoid that route.
