Ok, you don't even have to change the GUI if you:
Once you hit level 20 quests of all levels are shown in the compendium.
Once you hit level 20 quests are sorted by epic level instead of heroic level.
That shouldn't take long to code.
If you want to add a level of flare you can add a checkbox toggle in the options panel for it.
If you want to add another piece of flare you can add a toggle in the GUI [ ] sort by epic level.
Please?