As of Summer 18, I don't believe there is any way to do mass actions directly to a (Lightning) Action.
My current workaround was to create a Visualforce button, use StandardSetController to shuttle the IDs in a format for
lightning:navigation to understand and finally redirect to a lightning component (that takes up the entire page) with the new
standard__component navigation parameter found in the new pageReference types documentation
P.S. your VF page with StandardSetController will be responsible for the redirect. You can use the VF sforce.one navigation and create a url that
lightning:isUrlAddressable can understand.