>Which is a thorny issue because even if we assign them rights, they themselves will be the intellectual property of someone else. An intellectual slave?

Its not that novel. Take a Corporation it may hire an employee, or contractor - or even unpaid intern - and have them develop copy all day long. That copy will be owned by the Corporation in the future, even if the employee/contractor/intern ceases to work for said Corporation (even if said employee/contractor/intern ceases to exist their work will be owned by said Corporation).