We all know how the 5th generation went. All the big game companies switched production to 3D games, with only a few franchises like Castlevania and Kirby remaining fixed to two dimensions. Nintendo revolutionized the 3D game with classics such as Super Mario 64 and Ocarina of Time, but ultimately lost the generation.
What if there weren't a 15 year wait between 2D Mario games. Nintendo made a couple of 2.5D platformers, including Yoshi's Story as early as 1997 and Kirby 64 as late as 2000. What if, say New Super Mario Bros were an N64 launch title instead of Super Mario 64, complete with 4 person coop?
Would Nintendo have sold twice as many systems, as suggested by 2D fans such as Malstrom? Would 3D gaming have taken a major hit without a Mario game to lead the way? Would other franchises such as Zelda also have remained in 2D?
I think this is a very interesting alternate history, worthy of investigation.
Love and tolerate.