It would be cool to see a gradual increase in each content concept. One thing that lacks with XI in that sense is they sorta just threw concepts into the game and then negelcted them. The Most notable ones would be MMM(once abyssea was released), Ebon gears(synergy augment with special orbs that was to time consuming to be worthwhile) and pankration to name few.

It would be cool to see an MMO that's able to build a core concept to each mechanic so they can easily add on to it instead of having to write it from scratch each time.

In the sense of raids and instance dungeons one thing I'd like to see is "unlocking" new dungeons by compelting certain dungeons. It was mentioned that the dungeons would have different routes with different rewards and challenges to them. Though will there also be hidden areas that you have to keep an eye on to unlock, perhaps defeat certain foes of find a key from a mob at one point. With the key in mind it would also be cool if possibly upon fighting a boss mob it has a chance to drop a KI that unlocks a new dungeon to explore. There's just a lot of different ways to go about it and one should also remember that maybe the reward for completing a dungeon doesn't have to be gear 100% of the time.

A few things that I think would be cool for rewards could perhaps be a scroll that tells of a secret technique for a certain discipline, maybe the ability to abstract the bosses soul creating a job trait based on the bosses mechanics, just keep in mind there's more then one way to reward a person. As dungeons and raids expand I'd like to see a wide range of rewards ranging from gear, skill, traits, unlocking new areas etc. It would definately add a nice element of excitement wondering what each dungeon has to offer and which dungeons may have a secret ability that your discipline can use.