The new Proving Grounds coming in 5.4 look pretty neat. I think teaching players how to tank and heal without throwing them into a live group will be a good change.
I'm rather amused that, for the healer challenge, Blizzard included a hunter who stands in the fire and a mage who yells for heals. Good preparation for actual group content.
There's been some concern that the Proving Grounds will be the new "requirement" for guilds or pick-up groups. I think that it will actually be good for the game if Proving Grounds become the new requirement.
The current credentials required tend to be a catch-22. Usually PuGs are asking for people who have already done the instance, or have gear from the instance. So you require the help of the group to get the credential that will allow you to join the group.
In contrast, Proving Grounds are a credential that you can earn on your own. That makes it a much better credential for people looking to start raiding.
Pugs will always require some sort of proof that you are skilled enough to be successful at the group. Proving Ground completion is in some ways a superior form of proof to the two current methods. Thus, I actually hope that Proving Grounds become required by PuGs, supplanting gear and instance achievement checks.
To put it another way, if you're looking for your first job, and everyone requires 2 years of work in the same field, you're going to have trouble finding a job. But if employers are willing to substitute a degree or certification requirement, that can make it a lot easier to break into the field.
(Of course, you're going to run into problems if employers don't feel that the degree or certification matches actual ability. Then it's just a waste of time and money.)