I think that the world is vivid enough and populated with enough things that if they wanted to ask some more questions about the essence of humanity as seen through the eyes of a machine, they could do it.
What about a movie purely from a fugitive replicant's POV? Or a group of fugitives? What about a movie that shows more than just the xenophobic metropolis we witnessed in the first movie? What about a film that explores what replicants are used for in other parts of the world? The universe? The injustices they suffer and face because they're machines? What about larger sized independently thinking machines that are used for things like mining operations? Intelligent military drones that have been developed using the neural processors of replicant technology? What about replicants using cyberspace to escape persecution, moving their consciousnesses into new bodies through virtual functions in order to, effectively, live forever? Replicants building replicants, an allegory for parenthood?
Granted, this subject matter would have to be handled in a certain way to not seem like pandering or proselytizing. That's why they need a writer that will give Scott something he can't fuck up.