I actually don’t think this is true. I think that the HD660S was a genuine attempt by Sennheiser to improve upon the HD650. Indeed, I think they successfully addressed a number of the criticisms that had always plagued the HD650 - too warm, too slow and laid back, too much upper mid bass etc making the HD660S in many ways similar to what people who were modding the HD650 we’re aiming at. Somewhat ironically it was the HD650 modding crowd who were some of the least enthusiastic about the HD660S. The problem was that in achieving many good things with the HD660S they unfortunately sacrificed the detailed smoothness of presentation as well as some of the naturalness of timbre of the HD650 - the very things that made them legendary in the first place.
Fortunately, Sennheiser listened to the feedback and changed their mind about discontinuing the HD650. Additionally, I don’t think they could possibly have been planning the revised versions back when the HD660S came out.