You should probably focus on the already existing market, anything else is a waste of time unless Apple has invited you to prepare something. Otherwise that's just a whole lot of wasted resources on an unsure userbase.

Are you just working in Unity in the hopes it'll be an easy port? How could you expect to target this device knowing nothing about the platform?

It would be shocking to me if apple released a AR headset without at least considering Unity and/or Unreal support. Think about how long it takes to make a proper VR game, let alone a quality one