Redoing the effects work for TNG would probably be the easy
part. The real monster is to go back to the original film elements and re-edit the episodes. The only complete versions of any of the TNG episodes are on SD video, which, as stated, don't even look so great on regular DVD. They'd have to dig out the original 35mm film, then find the original editing notes--if they even exist anymore--dropping in new effects as needed. Essential they would have to completely redo the post-production of every single episode. This would be a huge amount of work and a huge investment of resources. And if those editing notes don't exist then the best they could do would be to create approximations of the original episodes.