A summary-of-plot journal could easily accompany this addition. Just a short commentary on what just happened in the story and where you need to go next, and a brief narrative of everything that's happened up 'til "now" in the game. I mean a better one than the one on the loading screen, because 9 times out of 10 that one is wrong: I haven't done what it says yet, or it's way behind.
I'll mention a couple more reasons.
Non-Basic speaking aliens talk really fast. I'm a slow reader. 'Nuff said.
Frequently, I will see things in the chat like "lfg *insert butchered quest name here*" while I'm not too far into questing on the planet. I'll know I'll have done some heroics on the planet already, but heck, I won't remember what their names were. I end up having to ask "Which quest is that," because if it's one I haven't gotten to yet, I want to join the group for it. Because we all know there's only one guy looking for a group on any given planet every 45 minutes. And I sure as heck don't want to wait around once I catch up in quests, saying the same thing over and over again, annoying the other 3 people on Balmorra that apparently don't like heroic quests. But I digress. With a quest log I could just check, "oh, hey I haven't done that one yet. Yeah. I'll join your group"
The completed quests that stemmed from other quests could be shown branching off from them so that you could see a through-line of the side-story. Or just for a small sense of accomplishment whenever you look at them. "Oh, hey, look. I did all those quests. Look how cool I am."
