Let's say that a player with a max-level character cannot raid for whatever reason. How then should she advance her character as the game progresses?
Options
There are three options.
1. She can't advance.
Also known as Vanilla WoW. The players only option is to quit or reroll a new character. This is a potentially viable solution, but the viability depends on how many people end up quitting. This option also probably has the highest "conversion rate" of raiders. If the only way the player can advance is raiding, than a lot of people will give raiding a try.
In all honesty, I think that this option might actually work better now than it did in Vanilla. Because of the 10/25 split, and the normal/hard mode split, it might actually be a lot easier to get into raid groups, or convert smaller guilds into raid guilds.
2. Advance through new content at her level
Blizzard makes new 5-man content. But new content costs resources to create, and there is a finite amount. As well, each "tier" of 5-man content fragments the player pool further, and makes it harder to assemble groups.
3. Advance by repeating existing content
Essentially running the current instances and either upgrading the gear that drops, or giving points to purchase better and better gear.
Analysis
Obviously, Blizzard has chosen a mix of options 2 and 3. New 5-mans are released every so often, and as the raid tiers are added, you can get better gear from Valor Points.
There is one further point to consider. Does advancing her character mean that the player must earn the best gear, or is it enough that the player only earns better gear than what she currently has?
Consider the idea that Valor Points don't exist. A non-raider would have gone up to i346 gear with some i359s from reputation. When the troll 5-man instances came out, she would upgrade all her i346s to i353s. When Firelands comes out, she upgrades those i353s to i359s, which are now available for Justice Points (which reset when the new raid comes out).
Would that be enough advancement to satisfy the non-raider?
Personally, I think it's good enough. And it has the side effect of removing Valor Points from the game. Let raid loot drop from raid bosses. If you want the best loot in the game, you get to deal with the random dungeon generator, as in Vanilla. I would change the Tier tokens to a single token for each armor type, and that would be enough. When Firelands comes out, those tokens can go on the Justice Point vendor.
This would be cleaner and simpler, and remove the need for over-geared people to run heroics. Heroics would remain the province of those people who needed to run them. People wouldn't expect everything to be AoE'd down. It would also have the side-effect of encouraging more people to try to step up to raiding, rather than just grinding heroics. But heroics also offer loot one step below the current raid tier, keeping a heroic geared character a viable recruit for all but the very edge guilds.