Checkpoint respawns comes with a bunch of exploits and problems, so not for now. Maybe if runs with respawns are not added to the leaderboard.
What angle pieces do you have in mind?
The bob sleigh looks pretty cool. I'll look into it!
I Can't Respawning at Checkpoints. Can Respawning Only Start
Is the Most Respawning on PolyTrack is Start
Maybe make special checkpoints that you can respawn at to not ruin the old checkpoints