Happy Home Designer isn't just on the 3DS, it's on the switch. Happy Home Paradise IS Happy Home Designer. It is a sequel to it. Even though they added it as DLC and need the base game, it's practically a whole separate game. It just also integrates your New Horizon's island so you can redecorate your villager houses.
I'm sure they'll add a version of that to the next Animal Crossing game due to how popular HHD and HHP is.
