i doon't see the difference from your suggestion, to the current system. I mean if the GS drop on a scale from 1 to 9 about too point,s, or at a scale from 0-20 for 4 points is relativ the same. When i expect, that GS 20 is similiar to 9 here, and the scale is nearly 2 for one.
If the gs difference is managed like today, so that GS 18 to 20 is like the difference from 7 to 9 then you have to watch your minutes even more carefully.