The RL doesn't sell because its a big, steaming pile of
sugar
honey
iced
tea.
I'm sure Acura knows that they weren't/aren't going to sell many RLs. They know their bread and butter lies in the TL/TSX/MDX sales. As far as I'm concerned they are doing okay with the car, but they could do more to establish the RL as a car they actually intend to sell instead of being okay with it's seemingly halo car-like status.
I'm keeping my eyes peeled for a V8 option (long shot) or a car that will sit above the RL and assume flagship status allowing the RL to better compete with the GS/E class/5 series/M.
Although, if Acura releases a big luxo barge...a V8 would seem like a foregone conclusion.