Class Keystones

What if Riot were to make keystones/mastery trees specifically available to only certain classes.

Pros

1. NOTHING NEW! Riot already has champions identified in classes based on scaling/stats: Marksman, Tanks, Mages, etc, so identifying masteries for classes wouldn't be a complete new project.
2. FOR THE NOOBS! Choosing masteries would be a more welcoming task when coming to beginners considering the guides given by Riot are already vague as is.
3. BALANCE! Creating new keystones/masteries would be an easy task for Riot with the new system because other champions would not be able to abuse keystones/masteries that are meant for specific classes along with less frustrating gameplay/champions feeling unfair.
4. CHAMPIONS FEELING GOOD AGAIN! Current keystones/masteries changes could be reverted and not suffer significant nerfs due to other classes abusing said keystones/masteries, (Tanks in solo lane with CC abusing Courage of the Colossus that was meant to support supports who receive shared xp and gold, as well as bruisers abusing Fervor of Battle.)
5. REWARDING GAMEPLAY! Gameplay with champions with specific class only keystone/masteries could receive a more rewarding gameplay for contributing to their team the way the champion was made to do so, (Marksmen AA'ing enemy champions and taking the risk but staying in range with a more powerful Fervor of Battle, Mages landing multiple skill shots to proc Thunderlord's Decree, Supports initiating team fights with CC and being granted survivability with Courage of the Colossus.
6. ? Any thoughts I may have not thought of ?

Cons

1. CAN'T STRETCH! Specific class keystones/masteries would result in less flexible gameplay and perhaps make the game feel stiff/restricted to the players. (**FIX! **Without the fear of allowing other classes to abuse keystones, Riot has the option to create multiple keystones/masteries for classes, widening the options and making the game feels as felxible as it did before/ having certain keystones/masteries "Universal," available for multiple classes.
2. ? Any thoughts I may have not thought of ?