You posted while I was finalizing my post about Rawtherapee, so sorry for the duplication. As to the last point, all they would have to do to avoid unnecessary complication for less experienced users would be to include a small icon to invoke the raw histogram as shown below for RT. This would avoid many trips to RawDigger for more experienced users.
No problem, we just expressed a similar thought.
I agree that it shouldn't be too difficult, but I also know that sometimes simple things can be complex to program. Anyway, let's hope Adobe is paying attention. The RawTherapee implementation doesn't create too much clutter, it's a toggle, so that can't be what's holding them back.