We (SharpTools) have been working with SmartThings on the new Rule API, but primarily for the Rule Engine part of SharpTools.io.
We were privileged to be part of the limited Rule API pre-release leading up to the last Samsung Developer conference and are excited about the possibilities it will bring - especially the future possibility of locally executing rules.
The Rule API is really designed around rule/automations. The being said, even the Rule API does not run locally at the moment (though there are plans for parts of it to run locally in the future).
At the moment, no dashboard is going to run locally with SmartThings. While HousePanel hosts the files for loading the dashboard app locally, the integration itself requires a connection to the SmartThings cloud - both for device control and device status updates.
Similarly, both SharpTools and ActionTiles (and any other app integration) communicate with the SmartThings cloud. Even the SmartThings Mobile app itself requires communication with the SmartThings cloud.