I respect people who love the AP's on the Nord, but I struggle with these "love-in" threads about new sounds. You could probably just take any upright sound and lower the highs and it's now a mellow piano.
It seems like you're too caught up in the brands.
I think each of the Nord pianos (grand and upright) have characteristics that differentiate themselves from one another. They may not be apparent on first listen -- they may not even be readily identifiable as a specific brand characteristic -- but they don't all sound the same.
Ultimately, the goal is a convincing and highly playable piano sample, right? The Mellow Piano is all about vibe
, not brand name.