Microsoft likely would enter the race, inspired by Sony's PlayStation. Even if the PlayStation loses to the N64, it would still put up a heck of a fight. I wouldn't even be surprised if Sega Saturn is the end of Sega, and they have no Dreamcast.
So setting the 6th Gen up, we have a DVD-compatible GameCube with backwards compatibility. PS2 would likely still give a huge fight, even if they lose. PS2 would have year or so lead on the GameCube like in real life. That would give the PS2 an early advantage. I also see the Grand Theft Auto series doing insanely well and bolstering the PS2. Even if GTA still comes to the Xbox and now the GameCube, it will likely stay a timed-exclusive on PS2.
I don't see the Xbox selling much more than it did in real life. Microsoft still releases the 360 in the 7th Gen, but I don't see them making it to Xbox One.
Lifetime Sales Predictions
Switch: 125 million (was 73, then 96, then 113 million)
PS5: 105 million Xbox Series S/X: 60 million
PS4: 122 mil (was 100 then 130 million) Xbox One: 50 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima