If Epic Characters aren't allowed to run ANY Heroic Quest on Reaper will Dreaming Dark count as Epic?
You will also significantly hurt the Lvl 17-19 Base Lvl Heroic Quests that are already hurting more than most due to Epic Normal XP being so much higher than these give on E-BB!
Suggestions:
Use BB rather than a Strict 2 levels above base - That way Lvl 26+ Quests would all count for Capped Toons to run in Reaper rather than 28+
This gives Capped Toons WGU for instance.
Expand the Epic BB system down to Base Lvl 17 to allow Lvl 20 Characters to run Lvl 17+ Quests on Reaper {AND Elite BB} rather than 18+
This reduces the heavy disincentive to running Lvl 17 Quests.
Raids should be EXEMPT or have a much wider Range allowed depending on the Raid.
Abbot for instance regularly STILL wipes Epic Groups on Elite never mind Reaper - Unless you're going to give us Legendary Abbot you might as well just make this Raid Exempt from this rule.
It's brilliant that you've decided that Reaper should have significant Overlevel Penalties and even a Lockout BUT you may have gone too far and been too strict.