Here are a few nice-to-have functionality to include in Actors.

1. Extend actors to include collisions - allows actors to collide with objects in the environment.
   • may require updating physics systems to support actors
2. The SDF spec says that <actor> can include <joint>s but this is not supported yet.
   • Note I think this is also not supported in gazebo classic
3. Extend actors to support nested models?

To have feature-parity with gazebo classic, we'll need to implement 1.

Additional context

#1947 (comment)