As much as I am excited for Runes Reforged
I feel like it's just going to be like the current masteries system where we have choices, but it's just going to come down to meta and whatever keystones are meta is what everyone is going to follow and Riot is going to fail again with the playstyle deciding aspect of the game.
I may just be pessimistic, but when keystone masteries first came out Riot had that same mentality and it just turned into everyone using the same masteries for the same champions (Thunderlords used to rule this game). I really do like the effort to try and introduced more variety into this game, but it's so hard to accomplish that when a meta is so strict.
Only keystones I can really see accomplishing a play style decision are Support keystones since Supports champion kits are all different compared to ADCs or mages.