I've recently leveled an alt and there is a requirement to do Garuda/Titan/Ifrit HM before starting the story for patch 2.5. It was not a quest objective, but rather a hard requirement to begin ARR finale quests.
Speaking of that alt... I've finished ARR and am now past level 35 on a Heavensward job, while I still have a sprout icon! I would be sad to see the existing story become shorter. Maybe there are some unimpressive fetch quests here and there but it makes the important stuff more meaningful.
But indeed as Vidu said, the level 50 story will not be required for the next expansion. I'm glad they found a way to please both camps. No story arc will be butchered but people also don't have to play through all of them.
