You may or may not remember that I made it my hunter ranger's goal to re-do all the quests in the original adventuring zones. After the whole project lay dormant for a couple of months, I picked it up again the other day and was most annoyed by how difficult it was to stay on track. During the Protector's Jubilee XP bonanza I outlevelled the zone I was working on at the time, causing all the quests to "go grey", which - following the example set by WoW - caused all the exclamation marks above nearby quest givers' heads to disappear, forcing me to repeatedly click on every NPC in the area to see if a new quest had unlocked. I repeatedly ran into dead ends when I lost track of the main chain and suspect that I missed more than one side quest this way.
I'm glad that SWTOR never had a system like that, even before they had level sync and when low-level quests gave virtually no rewards. Some of us actually care about seeing the whole story, even if we're overlevelled for it! The disappearance of those quest markers is even weirder in Neverwinter, where grey quests actually continue to give pretty decent XP. I suppose there is the potential for confusion if later quests recycle an old area and players could get old lowbie and new high-level quests mixed up, but that could be solved by at least having a "show grey quests" on/off toggle like they introduced in WoW later on.