I will start off by saying that gated content makes sense, as long as there’s a catch up mechanism and that it is not obtuse. Burning Crusade was neither of these things and had one of the most convoluted key-ing structures, so much so that it required a large guide to get through.

Seriously. Look at this thing!
FF14 isn’t a whole lot better, as you must go through every single group event to get to the recent content. Not so bad for people that have been away, but for new players it’s a massive slosh through content that people are facerolling through (yay relevant groupfinder!). It’s not complicated or difficult, just long.
The old-TSW had a gating mechanism where you needed to beat a single boss given, with a given role (tank/heals/dps) in order to enter group content with that role. I thought it worked rather well, as it was a test that you have both the proper gear, skills and situational awareness to do more than just press 1-2-3.
Mists of Pandaria brought the proving grounds. A tiered challenge system where you fought waves of enemies, using a specific role (tank/heal/dps) and received a rank at the end. Bronze was to check if you had a pulse, silver that you were paying attention, and gold that you understood all your class abilities. It’s been in the game since, though more as an afterthought in order to allow people to test more than just combat dummies.
Mage Tower
Since this goes away on Tuesday.
There are good things and bad things about the Mage Tower, and that changes depending on your personal view. It was very challenging, requiring a high level of skill or a high item level (sometimes both). It was time gated, so that you only had a limited time to try it out, until the next window appeared. It rewarded cosmetic weapon upgrades (of varying quality). It required a significant investment of time to even scratch the surface. It was 100% solo, so you were left to your own devices to improvise.
If you think about it, this was really Proving Grounds 2.0. Can you play your class and role at top tier levels? The rewards couldn’t be power, since you needed power to actually beat the challenges – cosmetics are a great alternative.
And it was a pretty solid success, all told.
Forward
BfA does not have class-specific raid gear. All plate wearers are going to look the same. Which is a bit of an odd one, since top-tier raiders often pride themselves on the look of gear others cannot acquire, and the class that they picked.
Still, it’s an option for a new Proving Grounds mechanic to offer cosmetic rewards. It’s a further opportunity for these proving grounds to be used as a gating mechanism for group content (LFG/LFR), and allow the difficulty of group content to be pushed up a tad.
The downside to this is that it doesn’t allow for coordination between real people. But at least it brings up the skill floor to something past “just breathing”, and can help people better understand their class and overall game mechanics.
