They're really pushing the former racers in the bonus clips this year. Steph & Kristen's "Backseat Driver" recap series with past teams from all seasons, the coincidental(?) meeting with Hal en route to Regina.
For those who can't see them, by the way, these were the teams featured (copied from Steph & Kristen's Wikia page). The rest were them alone.
-Episode 2: Brent & Sean (Season 3)
-Episode 3: Frankie & Amy (Season 4)
-Episode 5: Rex & Bob (Season 2)
-Episode 6: Hamilton & Michaelia (Season 3)
-Episode 8: Hal & Joanne (Season 1)
-Episode 10: Holly & Brett (Season 1)
If they have one more season in them, I'm sensing hints from this that we're quite possibly getting an All-Stars next to end it off. After 5 seasons, there's enough memorable teams to fill a cast IMO. Vietnam's 5th one was.