I really love the new dungeons in Heavensward but was disappointed that the High Level roulette didn't seem to have the level 51-59 dungeons.

Perhaps a new category of roulette could be added?

Low Level (Pre-50 dungeons as you unlock them)
Mid Level (Level 50 NM/HM dungeons)
High Level (Level 51-59 Dungeons)
Expert (Current 60 dungeons and future Hard Modes)

As the level cap gets raised, the categories could be shifted around.
Just an idea!