The original TOS effects were included on the Blurays, the same could be done for TNG.
They were on film though. Remastering the TOS episodes would be remaster whole episode from film, then replace effects shots.
TNG would be recreate the episode from original recordings (hopefully all sorts of deleted scenes would turn up in the process) then recreate VFX shots. To include the original FX would mean upscaling that footage and inserting in the new HD master.
People keep repeating this erroneous info. Others have tried to correct it, and now I'll try. It's probably futile...
The effects were shot on 35mm film, too.
It's the compositing, editing, and the beams, lights, etc. that were done at SD resolution on video.
So, all the shots of ships, etc. were done on film.