The scaling is a welcome change for me as it feels more like a game. One problem though is that WoW is all about gear as part of it's progression system. I think they should make the heirlooms only have the XP bonus and not be pieces of gear, but something else. They could potentially make it a permanent "enchant" to a gear slot similar to how glyphs work. You could then change items in and out and they would get the boost.
I think it's a missing piece of feeling like you are getting more powerful when you get a new piece of gear. Right now getting gear only matters for the appearance unlock.
Thoughts?