Currently we need the entity exist first before checking if it can sling or be slung.
My usecase is, determining which helicopter to spawn in order to sling an existing vehicle. However the inverse is just as applicable. For instance determining a list of ammo crates that can be slung by a certain helicopter in a crate-spawner menu.
This is not a priority or very important, just a nice-to-have.
Honorable mention to this command too: