Greg,

We have been working on support for abstract method invocation from Skuid via JavaScript and the Action Framework, but this is not fully ready yet.

At this point our plan is to allow you to invoke methods of either Process.Plugin or @InvocableMethod , if not both — in my opinion it is ridiculous that Salesforce added another"abstract method invocation" paradigm when they already had somethign going with Process.Plugin. They decided to implement a new way to do things rather than making their old way better (see the comments at the top here). So now if you want to run custom Apex logic from Visual Workflow, you have to write Apex Code that implements Process.Plugin, but for it to be used in Lightning Process Builder, it has to implement @InvocableMethod — Salesforce could have reused Process.Plugin for both of them, no problem. Probably had something to do with Lightning Process Builder not being as native to the platform as Visual Workflow was required to be. Thus the fact that @InvocableMethods are only “invocable” via the REST API and not via Apex.

Okay I’m done with my rant

Either way it will be awesome.