Personally I feel that the class quests in FFXIV are the best storyline-based content included in the game, even better than the main story (not to mention some of the best quests I played in any MMORPG).
To improve the game, IMHO, the dev team needs not only to revamp what doesn't work perfectly, but also to expand and put in evidence what works very well, in order to play on the strong points of the game.
First of all, the class quests are not very visible. My girlfriend just started the game recently, and she didn't notice her story quest until I told her. I'm quite sure she's not the only one.
That's why i would mark the class quests with the (!) marker exactly like sidequests when they get available.
In addition to this, I think class quests start too late in a player's career, and there are too few of them.
I would move the quests (currently at level 20, 30 and 36), to level 10, 18 and 26.
Then I would add another three for each class to expand further on the story of each guild, reaching more epic proportions as the level grows. I'd locate them around level 34, 42 and 50.
I would also revamp rewards:
each quest shouldn't give just the guild marks (that at the moment are a bit overabundant anyway), but should award skill points for their specific class (I'm actually of the opinion that every quest and sidequest should *without fail* always reward skill points. Quests being part of the leveling process is now an expected and solidiefied staple of any MMORPG, and people get disappointed and annoyed when they finish a quest witout receiving a reward that contributes to their level progression. Currency is too low-value to be considered worthwile).
I would award, with every quest the following prizes:
2000 guild marks
15% of the SP necessary to level up from the rank at which the quest becomes available.
The level 50 quest should be more challenging and epic than the previous ones, and (since SP rewards aren't valuable anymore), should give a special and prized reward. I would say somethig equivalent to the Artifact Armor of FFXIV, warable only by the specific class and only at level 50. It would also serve as an incentive to reach level 50.
If artifact armors are already planned as prizes for other areas of content, then I would reward the player for the level 50 class quest with an "artifact weapon" of appropriate power.
Having an extensive and rewarding questline to look forward to for every class would also encourage players to play different classes more, as just three quests that give only a few gil and guild marks as a reward might not be seen by many as worthwile.
Finally, I would involve in the final three quests (the ones to be implemented anew) each player's path companion. As I feel that the path companion is an extremely valuable idea and asset to the game, and should be considerably expanded upon (as explained in this thread).
Thank you for reading.