If I pass an object, a list of objects or an attribute as a return value for a microflow, it should just be able to read the entity type or attribute type automatically.
Not sure if this fits in with your idea: but if I set return type to object (or string or list or whatever), and select entity "X" as return object, the value should be prefilled with the first variable matching the return type starting from the end event traversing towards the start event (for all end events).