I like the idea for Witch Bolt - though I wouldn't say no to the reactivation remaining an action if it scaled with the level the original spell was cast with either.
I thought the same thing, but making the reactivation of Witch Bolt a Bonus Action allows for spell weaving with other spells, which feels thematic to me.
Imagine if you could use polymorph on an ally to turn them into a minotaur, or an ogre. That would be cool. Gale smash!
Agreed. I think a control spell such as Polymorph should offer many different possibilities to control the encounter as you see fit. Turn an enemy into a sheep or turn in ally into a beast (obviously needs to be balanced accordingly).