Why its a good idea:
1.) It’ll be less annoying (don’t need a god damn quelling blade on every hero)
2.) It makes the spell more interesting. It can be used either offensively or defensively and you can still trap heroes by using terrain to your advantage.
3.) You can finally buff treants and get rid of this god awful 4-4-0 build
Visualisation:
But how will all the brain dead NP players play if the ability is vector targeted