That is if Pa3x 61 keys was not meant to cover that need.

Honestly, what else features wise could be in between Pa3x 76/61 and this new Pa600 to such extend that will justify yet another product?

Ok, I am probably wrong, but that is a possibility I guess. Time will tell. Now I am just curious whether Pa600 will be much more expensive than Pa500 or will it keep the same price range - it should, as it is defined as entry-level.