Fundamentally, they would need to redo all the post-production work from scratch. Probably doable, but expensive. There's no middle-ground - as there was with TOS - of playing with the edited episodes, where film prints existed of the final episodes that could be "cleaned up".
Blame Berman's right hand, Peter Lauritson. He is the guy who made the call early on to finish on video, knowing full well how it would hamstring things in the future -- and for a property already known for its longevity, that seems so far beyond criminal to be just terminally stupid.
Oh, the other poster ... TNG did NOT do planet projections in the first couple years, those are all photos mapped onto a circle or sphere in the computer. Projections would have looked a ton better than that, those scanned pics at times looked out of focus, and worse than almost any original TOS planet (except of course the Rand McNally looking monstrosities when they orbit earth.)
All this is covered in Cinefex -- either issue 37 or 38, I forget which.