This post https://developer.salesforce.com/blogs/2018/01/introducing-sample-components-lightning-component-actions.html introduces Sample Components for Lightning Component Actions, with the stated idea being these are solutions to replace JavaScript buttons.  It also states to post questions to this group. 

One example is a Mass Update example, but I do not see a Mass Update from List View custom example. 

We'd like an action/button to launch a component, from a list view, in the overlay, and have it provided with the selected/checked records. This was a common use case for JS buttons on list views, using something like var selected  = {!GETRECORDIDS($ObjectType.Case)};

Is this possible?

I do see https://help.salesforce.com/articleView?id=cases_consider_lex_mqa.htm but it does not seem to work with LC backed quick actions.