Wasn't sure how to make this a suggestion, but I think a parameter to either allow spells to target armour stand and/or entity projectiles or allow them to be targeted by spells would be useful since it would for example allow projectiles to collide with each other or allow someone to cancel a projectile in the air without needing to target the caster or cancelling other spells.

Were you able to try this out? Could you get two projectiles to collide?

I tried it and they didn't seem to collide even with the tick area of effect.

You can do this via target_armor_stand: true on a spell.

I'm not 100% that'll make two different armor stand projectile spells collide... but it probably might.

This is mainly used in the war configs so you can shoot the cars and destroy them.

I had no idea about this, thank you. And for making 2 projectiles collide if normal targeting doesn't work then a tick area of effect probably could.