This is possible right now with Finder Folder Actions if you’re familiar with that.
Here’s a sample script to attach to that:
on adding folder items to theAttachedFolder after receiving theNewItems
tell application "Retrobatch"
set d to open "/Users/gus/Desktop/My Workflow.retrobatch"
execute input items theNewItems
tell application "Finder"
-- Optionally move the items to the trash.
move theNewItems to the trash
end adding folder items to````
Having RB watch a folder when a workflow is open is something I'm looking into though.