I think this is a terrible idea for one reason: there would be very little content for people to do post-50/51 through 55 (or the next level cap -5 ) if the Classic and current Level 55 Ops were constantly being re-engineered to be higher and higher levels.
Right now, class story nominally carries a character from 1-50. Ilum and Makeb could carry a character through from 51-55, but let's face it--with a single track, those can get kind of stale. They have the SM and HM 50 Flashpoints, but that and possibly Dailies would be it under this scheme.
I don't think the OP's idea is a bad one, although it would effectively be a NiM+ difficulty. But I'd wait and see how 2.4 and the two new 55 Operations there makes things.
I wasn't thinking of replacing the lvl 50 version with an updated version of the ops (like they did with TfB in 2.0), but rather having them exist side-by-side. There could still be level 50 versions of these ops (and level 55 versions of TfB/S&V) that are exactly the same as they are now, and then copies that have been updated for the current level cap.