Grading is constantly evolving. Who is to say that a few years down the line CGC (or some other company) may adopt a multi-tiered grading system that accounts for production quality, eye-appeal and restoration. (Don't be surprised if this happens when submission levels start to steadily decline. They have to find some way to get people to continue to slab a finite number of books... but I digress...)
As it has been noted, production quality varies greatly between books often creating a vast difference in the appeal of books which have the same exact grade label.
It would be interesting to see a grade like 8.5 / A / 0.0
8.5 structural grade / A production grade (perfectly cut and centered, bright inks) and the 0.0 is the restoration scale. My feeling is that the purple label stigmatizes restoration and puts books with tiny color touches or dots of glue in the same category of re-created franken-books.
For instance would you rather have a FF #1 that is
6.5 / A / 2.0 (slight color touch)
4.5 / C / 0.0
The way the market is now, the latter choice would be worth a lot more than the former. But on paper, the former seems more appealing doesn't it?
In any case, doesn't this system tell you a lot more than the current single number grading scale? And it tells you the level of restoration rather than simply stigmatizing it with a purple label.