Maybe replace the ARVR_Camera with a normal Camera node while developing, and then swap it again when you are ready to test in VR? That is what I would do.
I think Camera and ARVR _amera are almost identical as far as basic functionality goes. As far as I know the only difference is that ARVR Camera renders two views (one for each eye) and has head tracking, while Camera just renders one view without any head tracking. They should be fairly easy to interchange.
Also, have you tried running a nightly build of Godot 3.1, or Godot 3.1 alpha? Obviously using a nightly/alpha build is not necessarily recommend for production (because of bugs), but depending on your project it may be a relatively safe way to start your project while you wait for Godot 3.1 to be released.