Implementing this would be rather complicated in the long run. They'd have to scale all the abilities down to such a degree that your DPS (or other capability) isn't significantly different from someone who is at level for the dungeon and not level-synced. When you consider that a level 41 character synced to Haukke Manor has a different suite of abilities than a level 35 one or a level 60 one, the actual scaling of the abilities would have to have a ton of variations and the like. You might not think that's important, but if they didn't scale the abilities properly, newer players would essentially be punished by the community. While people might not go so far as to kick them, a not insignificant number of people would likely bail on runs that didn't have sync'd DPS, and the lower roulettes are meant primarily to help these players, not make them feel marginalized.

They could do something like have the change only apply to level 60s, which would reduce the complexity of the necessary syncing system, but it'd still be quite a lot of work.

All that being said, I would seriously love to have access to central abilities like Lustrate on SCH, Shield Oath on PLD, or Gravity on AST at lower levels. MNK also feels really odd without Dragon Kick. I'm just not sure that they could ever implement this in a timely manner--and the time they spent working this out is time taken away from other development areas.