An rxp increase won't make heroics much more played in high reaper. Heroics are played in fast difficulties because people want to get their PLs before they die of old age, there are too many of them, so if you want substantial progress, you can't just go smelling the flowers along the way, you have to go fast. And let's be realistic, playing high reaper when most builds don't have their defining abilities is a no-no for most people.
I have played high reaper on heroics for fun on occasion. I don't want to and refuse to do it on a regular basis. The two reasons are as stated above: it's more fun to do it in cap when I have my full build and when I do heroics, it's to get PLs, so I want to get them before I die of old age.