Pop-ups are one thing sure, but there is also one thing they have never even tried implementing and it's a quest journal not just with active quests and completed quest, but also quests integrated within broader series.
For example, take the Vanadiel raids: you pick up the first quest, it shows in the journal like today, but also under a greater "folder" called Vanadiel. Once you complete the first tier, quests show as complete, but the Vanadiel category still stays active, and the next patch that introduces new content, it should be blinking with a ! or one of those green dots indicating there is new quests and content, and pointing where is the next pick up. To me it's like, basic info and usability?