I don't think so - there have been no reports of any cable system offering expanded capacity period (extra cost or not). SA documentation, and any (knowledgable) statements from cable have talked in terms of "approved lists" of ext drives that the customer purchases. Its just that us followers of DILAMI are at the leading edge here.
By the way, the "copyright" issues are addressed in the SA design - the recordings on the external drive are encoded to play back only with the original DVR. Bottom line - the tech didn't know what he/she was talking about (surprise)!