Did the FFVI tech demo lead to an N64 release? No. Why should the FFVII tech demo lead to a PS3 release?
Personally I don't want there to be an updated version of FFVII. It would lose all the elements that made it such a great game all those years ago. SE should focus on getting FFXII released and then take their time in planning the next FF. I just hope they don't miss anything out *looks at FFVII*.