Agreed, though WoD wasn't first and foremost a time travel expansion. The devs said they wanted to bring back Guldan (maybe some other Draenor characters too), and their first idea involved doing some crazy magic in Outland. The time travel route worked best, but they only did it to bring old characters back. They barely explored the idea of character development involving time travel. No one asked about their former selves, which is really weird. That's probably the first question I would ask a time traveler.
WoD's time travel rules were also pretty effed up. Rather than use the DBZ timeline-branching rules
, they went with multiverse branches. This means there are infinite timelines that exist, which sort of dilutes the importance of ours.
I still think that a time travel expansion, done properly, would be fun. Maybe Thrall could recover his pre-drained Doomhammer, or Arthas could return to work for the Voidlords. I would take this over BfA's faction yawnfest any day.