I'd very much like something like this aswell! Not just for the mainstoryquest but also for any longer quest-chain - Hildibrand, the Theologikum in Ishgard, the quest/cutscene-heavy quest-lines each area gets...
Just making a new character isnt really the solution here - sometimes I'd like to see just one specific quest again, that might actually require playing through 80 hours (or more...) of story/game that I dont want to see again.

Ofc those quests should have no rewards!