Well, that's just it, you wouldn't
have to re-do the effects in that case.
Yes, it would probably look terrible (about as bad as the difference between visual effects and other footage on the BABYLON 5 DVDs, in fact), but it would be an easier and cheaper way for CBS Paramount to release the series on Blu-Ray than redoing the visual effects.
I'm not sure, upon reflection, if CBS Paramount would treat the series like that, however. I certainly wouldn't want to see a release along these lines, but it might be a serious possibility if CBS Paramount decides they don't want to invest the money into the series that would be required to recreate all the visual effects.