What's the big fuss about these new remasters? What's the big gain...?
Remastering of music means that they take each separate track (i.e. bass, guitar, vox) and they set the levels of them again, as well as the fade and any additional effects (reverb, echo, sustain, etc.).
So technically a remastering of these albums could result a version of "Eleanor Rigby" where there isn't quite as much harmonizing on the chorus part, and the violins could be increased or reduced in level which would maybe make the bass line stand out more.
Or you could you could take "Taxman" and instead of fading the vocals way left and the guitar way right, you could balance them both out so that they don't have such the separation that we are currently familiar with.
These things are not likely to happen, and any "remastering" is probably going to be incredibly subtle to avoid any backlash. But ultimately that is what "remastering" is all about. I'm sure others will be glad to expand on my description.