http://www.misplaceditems.com/rs_tools/graph/
OSRS doesn't have "more" players than Runescape. It has several times its population. On peak hours there are around 140k online in OSRS, while RS3 only breaks 25k once per day.
And yes, if they were to take this approach and continue Classic WoW's story it would blow BFA's numbers out of the water.
"People don't want it", "People would vote for dumb stuff", "it wasn't in Runescape back then", "No one will pay to play a 2004 game", "The demographics have changed, that is why the population decreased, not because the game became worse".
All that crap was said, and the end result was amazing. Learn from Jagex, Blizzard. Save your own game.