When I said just doing what TNG has done, basically post production of all teh aspects of the show, on the FX side that would be more expensive with DS9. As each ship has multiple elements do it.
We have already had interviews talking about how TNG is getting harder to due thanks to the FX, and well time is money. COnsider that many, many fx shots in DS9 have far, far more elements then TNG's shots did. Again that means more elements to scan, to match up. Just takes more time.
I certainly expect that the motion control model shots wont be up converted.
There are two issues here. They can upconvert the files they already have just off the old standard edition master. It would look fairly poor.
Now they are also talking about files that have been found, and that if they can find enough of them they can for the most part just render them for HD without much work at all, just processing time.
Here we have no idea if the holders of those files are willing to let CBS use them/ or pay to use them. We don't know if CBS is willing to farm out the work if that is what the holders are trying to achieve (again have no idea, how much will be found, we have only heard from the supplier who did the least amount of work on DS9, though I was very surprised they worked on very light fx episode the Waltz, ect,e ct).
Certainly CBS could create less detailed CGI effects that were rendered for HD, that don't match the original shots. Just like they could also spend a huge amount of tiem and money to completely try to match each shot (very unlikely).
But my point is that CBS doesn't have to do anything to the CGI if they don't want to. THey can simply upscale, off the low definition master (we saw how that looked with models and live action, not very good at all). That would be the worst possible outcome (outside of no release at all). But it could happen.