Another thing I'd like to see regarding quests (besides an editor). I'd like to be able to fit more text into more screens. Right now, the only two places which are fairly unlimited are the initial opening quest description (upon accepting quest), and CompletionText (which appears you can't change the image associated with this, it appears to use the Image defined for the quest accept screen). QuestChoice only allows 400 characters. Being a choice though, we can work around this for now.
The other thing I'd like to see is some kind of allegiance tag within a quest condition. This way we can add flavor in quests depending on if you're a kingdom, or empire. I see the <Faction> tag in there, but it only resides in non-active quests right now. And it only ever has Player reside inside of it. Seems kind of redundant, as the player is always the one doing the quest.
Also, open up gamemodifiers to all parts of quests. This one can get very frustrating at times. I don't recall now, but there have been occasions where I had to move a gamemodifier from one part to the other. I don't remember the order at this time, but I think I had a gamemod in a questconditiondef, which didn't work until I put it inside a QuestChoiceDef. Very confusing, especially if you're just starting out creating quests. Even if there is no change here, providing a list of valid gamemodifiers for each container would be invaluable.
EDIT: I think, from talking to Cari_Elf, that you meant to have PopUpObjectiveMsg take care of long text. It does allow for a lot of text, however, as the name implies, it's a popup. And not a very large one. It only takes up the bottom part of the screen, with a medallion on the left side, shrinking the already small area for text. If you put too many characters here, the text will shrink, fitting it all, but making it nigh impossible to read.
EDIT2: Also, it would be nice if there were a way of having requirements for doing a quest. Or at least maybe not upon being able to accept the quest, but within it. Something like <TechRequired>Armies_Trogs</TechRequired> inside of a QuestConditionDef. I say this particular type of tech in this situation: A quest where you have quite a large battle, and you want to make sure the user can build troops before accepting the fight. This way, we can keep the quest active until the user has the appropriate tech.