Luigi was planned when 64 was meant for the DD. Got canned after that. Was going to be in 62 2, but that was scrapped again as the 64 DD failed.
And Paper Mario was planned as Super Mario RPG 2 for the 64, however Square Enuix left Nintendo for awhile and so we got Paper Mario. It had been in production since 1996 as RPG was a hit.
There, that's the history lesson for you.