Getting rid of Target inheritance entirely is not going to happen anytime soon.

But one strategy that allows us to move more pre-computation into the engine is to begin externalizing target arguments, so that the engine can compute more before passing them in... and then, eventually, not pass them in.

I think my strategy will be to define a series of Field instances as class properties of the relevant Target subclass, which the engine can use while hydrating a target to pre-hydrate its fields. This code will likely need to replace Payload (eventually).