This 
As I mentioned in another thread:
Webcore isn’t just a program written in groovy. It’s a program written to run in the environment of the Samsung-hosted groovy cloud, taking advantage of features and values not all of which were documented and not all of which will be available after the groovy cloud is shut down. The Rules API does not currently have feature parity with Webcore, so there are a lot of things you can do with Webcore that you just can’t yet do with the Rules API.
So just setting up a machine to run groovy and then communicate through the API doesn’t necessarily give you all the functionality you had when the same code ran in the groovy cloud.
I’d love to see somebody succeed at doing this, but if it were simple, it would already exist.
Still I didn’t think @ady624 would succeed in writing Core to begin with, and obviously I was very very wrong on that one. 
This is a very creative and talented community, so who knows? Maybe somebody can make it work.
I should add that thanks to @taustin’s excellent work on an MQTT interface on the new platform, that does open up some additional options, including using MQTT to get to Hubitat (which does run Webcore). But we still run into the issue of the stuff that smartthings does not make available through integrations. Tricky. 