Guest characters in RACING video games over others

When the topic of guest character shows up, everyone obviously immediately goes to fighting games, or maybe party games

Street fighter

Tekken

Tournament/arena fighters

&

Mortal Kombat

But what about racing games?

Who here wouldn't wanna see the Mystery Machine, baby the impala, or the ghostbusters' Ecto-1 in a racing game?

Who wouldn't want to seed the Mach's 5 & 6, and the BEATNGU truck from Jeepers Creepers in, oh I don't know, TWISTED METAL?

What vehicles would you all like to see in racing or twisted metal style "fighting-racing" games?