I thought you just meant the original 2D series. I don't consider it a part of those games, just like the Returns series isn't part of the original Country series.
I definitely think it's part of the over all main series though.
EDIT:
It's grouped it this way:
Original 2D
Super Mario Bros.
Super Mario Bros. 2 (JP)
Super Mario Bros. 2 (US)
Super Mario Bros. 3
Super Mario World
-
"New" Series
New Super Mario Bros.
New Super Mario Bros. Wii
New Super Mario Bros. 2
New Super Mario Bros. U
-
3D
Super Mario 64
Super Mario Sunshine
Super Mario Galaxy
Super Mario Galaxy 2
-
Isometric Mario
Super Mario 3D Land
Super Mario 3D World
-
I do think that they can make a new 2D Mario game that succeeds Super Mario World and continues that line, but I don't think the "new" series does that. I also think there can be a Donkey Kong Country 4.
