1. Lower the dificulty gap between Normal and heroic.
At the moment normal mode is incredibly easy while hard mode is exactly the oposite. This causes alot of newlystarted or mediocre guilds to think "hard mode is impossible" because the game doesn't provide a smooth learning curve for new players.
Basicly the first boss as a hard mode should be slightly dificult then the last boss normal and then bosses should become harder and harder as the instance goes on.
2. Make 2 instances per tier.
Alot of guilds that I know off have stoped raiding ulduar, just because toc gives better loot as they bring the "Why whipe for cheaper loot" mentality.
Its sad but true, alot of players do play the game for rewards or the promise of a reward and in many cases this comes from epics.
Having 2 instances share the same tier (like tk/ssc mh/bt) would increase the life span of both raiding instances, and also adds a bit more variety to the guilds raiding calendar.
3. Add a sense of progression back into the game
At the moment if I would start a new guild id begin raiding nax 10 then toc 25, skiping ulduar alltogether (wich is harder then toc btw)
While I understand new players should catch up to the end game raiding, people shouldn't be able to simply jump over instances. Otherwise one could just cancel his account untill the last raiding instance is available, play that then cancel his account again untill the next expansion.
4. Stop making instances puggable.
While I agree that every one should see all the content, they should do so inside a guild. Otherwise guilds will start to decline and experience alot of dificulties as players will realise they don't have to be in one in order to acomplish things anymore.
The keepers in ulduar were decent bosses that, while beeing easy, were also chalanging enough that most pugs wouldn't be able to clear them.
5. Stop showering people with epics.
The whole reason of epics beeing fun was that it took some time to gear your toon up. In tbc I've spend 2 months to get full t6 gear from mh and bt.
Now a days it takes maximum 2 weeks to gear up an alt to full epic making the excitment of geting a new item far less then what it used to be.
6.Make heroic 5 mans heroic again.
Add CC and make them chalanging. That way people can master their class a bit more and the experience of doing a heroic wouldn't be just "Gogogo pull gogogo aoe come on move gogogogo".