"Imagine the OOT with properly corrected colours, no grain/dirt and without any motion smearing... I don't recall the X0 team saying anything about being able to 'undo' the motion smearing "

Correcting the colors and removing the dirt is technically very easy (and is being worked on as we speak......er, type), but removing "motion smearing" is getting a little dangerous, as you risk adding visual information as much as changing it. I'm curious to know which scenes in partiular you are talking about, since motion blur can be a good thing (which is precisely why Lucas developed motion control.)