WWI brought the good news, or rather leaks did previously, that attunements may be a thing of the past, no more grinding to revered to get into that heroic, despite being in T6 gear, no more following through the progression in a linear way and never having the option to go see a different area. The question though is does a free-form game, and indeed a game without that structure really help initially?
The Karazhan attunement was annoying later in its life, getting people together to run three heroics, and not the most common ones at that, completing a long solo quest and needing your flying mount made sure that people who were running Karazhan initially were at least capable of functioning in a party to the extent of clearing dungeons, then the requirement to kill Gruul and Nightbane to access Serpent Shrine Cavern proved that you could successfully work as a raid with some movement skills and control of phase switches, Magtheridon and the heroics taught control, dividing the focus of the raid into separate groups and debuff handling. These attunement quests all seem to have been focused on making players at least semi-competent for entry into the T5 instances, they won't teach people to chain trap, to sheep mobs doing arcane whirlwinds or any of the esoteric things about their class, but they appear to have served a purpose.
The tier 6 attunements by contrast appear highly arbitrary, killing Kael'thas and Vashj to unlock Hyjal makes sense in a way, the faction requiring a token to prove your bravery or similar, but in truth it merely slows down the game by ramping up a huge skill and co-ordination test at the end of an instance of moderate difficulty. This massive ramp up though wasn't carried through, the first bosses appearing to lower difficulty considerably allowing them to be seen more as loot pinatas than as truly difficult bosses, though perhaps they were part of the learning curve, Rage Winterchill to give a reasonable example of trash waves followed by a boss, the lack of release and requiring raid movement and also survival for extended periods of time. Naj'entus appears to have been put in place again for raid movement, co-ordination and handling massive raid damage which we really hadn't seen before. However any raid that couldn't move and act independently didn't get past Magetheridon, Vashj, or Kael'thas, so adding these learning fights to the start of an instance appears to simply be a rehash and a reward for killing the previous bosses.
This setup works fine with the attunements in place, the ramp up restricts progress and loot, then the easier bosses immediately after let your raid gain some easy progress and pad the loot list of the pre-attunement bosses. Dropping the attunement then leaves people with a choice, face a difficult ramp up in terms of difficulty, facing a boss which requires a lot of co-ordination, learning and focus, or hit something easier in the next tier. This isn't really a choice for a lot of guilds, the slow reduction in difficulty of certain bosses leaves them ill prepared for the ramp up to these bosses, so skirting them becomes the operational plan, and indeed any of the harder bosses in an instance can be skipped for much better loot from the next tier with the difficulty ramp reset.
Badge gear clearly has an impact on this, the entry requirement to tier 5 was completion of a large part of tier 4 for a large proportion of your raid, tier 6 the same but from tier 5 gear. The level of gear suddenly available from badges effectively shorted this, allowing guilds to gear up in Karazhan and acquire badges, purchase gear, and effectively by pass any of the harder steps of tier 5 content for early tier 6. This caused a lot of outcry both in joy and sadness, the elitist feeling of being in tier 6 was lost as it was achievable by anyone. This though is really necessary for those guilds to survive since guilds tend to poach players from lower guilds to feed their recruitment and burnout rates (which tend to increase as content gets harder and faster). The badge gear however didn't give people a reason to return to tier 5 content, and led to many people feeling left out of that section of the game, or being unable to run it no matter how hard they try as the difficulty level is targeted beyond a random group and requires some leadership and co-ordination (which you learned in tier 4).
So attunements drove people to be capable of achieving in the next level of content, but at the same time restricted it heavily, adding badge gear and removing the attunements dropped these to allowing far less hardcore guilds to complete and experience these raid levels, however often left people feeling unprepared and left out / lost from missing a third of the game's end game content. Not having attunements is thus a better plan, or rather attunements that require huge focus and attention, slowly ramp up the difficulty, have the attunements teach the skills needed, but have the test of those skills the instance itself rather than the arbitrary barrier. This can be aided by lock outs and badge gear as we saw with the Sunwell, in that case it was another artificial barrier forcing a 2month clear on Sunwell, which could have likely been done in 2 weeks, what it did offer to the more casual raider though was a graduated levelling of gear and availability of epic gems. Perhaps in WoTLK we won't see the instances locked by tier, if your guild can kill Frosty the Snowman you can enter tier 9, but when you do so you will be tested as though you have experienced and geared from tier 8. When your server clears these challenges (or perhaps on a timer to ensure servers do not suffer from a lack of high end guilds), the npc's change and allow the purchase of badge gear in a similar progression to arena gear, as the difficulty of the "war" steps up so does the willingness of the npcs to help you defeat it.
This can be implemented at release by time locking the content, or by locking the content initially by rare drops in those higher tiers, you really do need frosty's carrot to purchase these items, because they are rare and hard to craft, when the server progresses and people perform the gathering, training and tier beating exercises then these drop allowing guilds not in that tier to make progress, however still making the entry barrier high enough, you may never see the tier 9 level badge gear unless you farm the tier 8 materials for it, but you can get the tier 7 ones which will let you progress into these instances, well, if you can handle the challenges they present and not the artificial barriers that might be imposed on you.