A lot of the interfaces for the pilots add complexity that could be reduced in the case of an autonomous aircraft, not just weight or complexity of interface. But actual complexity in the design and development stages. They also add constraints on expanding the capability of the system as new controls have to go somewhere, either displacing existing ones, changing the "buttonology" of the existing interfaces, or being tacked on to a mostly empty (hah) corner of the cockpit.

If we didn't have to care about those things, changing the existing infrastructure in an aircraft would be greatly simplified (not simple, but simplified).