This would greatly enhance turrets turret-like ability as well as make projectile better at distance and orbit for fast-moving entities. Possibly tier 3, made with bow/skeleton skull? Projectiles should home towards players/entities/blocks, orbiting projectiles could move 1 block (?) up, down, forward and backward as well as increasing and decreasing speed.

Some addons add this now, like Too Many Glyphs or Ars Elemental.