Will this work? And why?

Well I've been going through intense speeding/accuracy training doing riffs and scales over and over again (I've got no problem with repeatition, doesn't bore me).

But say for example I got one scale down and I can shred it, will that mean that... I can only shred that scale but nothing else? Or will be able to shred other things as well we little practise of course?

Mainly because I can't practise a lot of different stuff, and concentrating on few things, I hope this will help with my guitar playing overall.

You'll definately be able to blaze that one scale/lick you've practiced, but the benefit doesn't stop there. I have a few scales and licks that I practice more than any other, but when new stuff comes, it's usually a breeze becaue of the coordination I've developed by practicing these other scales.
Make sure that when you play these scales and licks that you focus not on ingraining this one scale in your head, but rather focus on how it feels to stretch two frets from your ring finger to your pinky on the third string using and upstroke, and then moving to that index finger on the next string with a down stroke. Think rudiments, not flashy lick, and you'll be able to tackle anything that comes your way with ease.