I'd imagine that the reason they'd do it is that they've already paid for the audio portion of the show, so that's one major aspect of production where they would save big bucks by recycling. They'd pay only small residual fees to all involved to simply repackage the old audio with new visuals, which would be dirt cheap compared to the cost of generating an all new audio track, with an all new cast, crew, musicians, etc, all of whom would have to be paid current scale.
CBS who owns the rights to the Trek franchise on television including (I would think) TAS is not going to make new Trek using the old actors. They will release new products of the old 6 TV series and feature films (like when they re-release the Trek I-X films for a deluxe edition with more restorations around 2016).
Dirt cheap is not the legal department headaches of relicensing the music and the vocal performances for 22 episodes for syndication, home video release, digital download, future media, etc.
Dirt cheap is not CGI for 24 minutes for 22 episodes= 528 minutes = 8.8 hours of 1080p CGI. Check the budget of
Tron Uprising on Disney XD airing this summer which should be 22 minute episodes.
Since TAS has not come out on Blu-ray I can see
only a possibility of doing a CGI version of it by CBS Digital as a way of selling TAS on Blu-ray
"with all new 1080p CGI VFX in full 16x9!". Of course on the Blu-ray there would be an option to watch the original animation in HD (or upconverted standard definition). Otherwise it is going to be a harder sell for 22 episodes with very repetitive music and some actors voicing multiple characters in an episode. Could you see them redoing the music score too with a modern sounding VOY/ENT score for every episode? How about repurposing those music scores and relicensing them too? They would have to pay residuals to every musician...
Can you think of a single example of that ever having been done with an old animated series in the history of tv?
As far as repurposing a cartoon series:
Space Ghost Coast to Coast
The second season of Space Ghost saw a boost in production values that made the first season feel like repurposed animation. Featuring more than 328 CGI sequences and an actual, live dinosaur, this was the season that made Adult Swim think differently about budgeting.
which is sold by
Adult Swim.
Can you think of a single example of a TV series being re-edited from edited takes with 10 second handles from the original filmed camera negative to match the original episodes? That is what TNG-R did for 7 seasons of a TV series.
Trek is a very profitable franchise for CBS and TNG being a particular property that has still a large audience and a future audience and they wanted to really capitalize on that.