Can we overhaul internals of Variables

[NickCrews]

@fgregg how open are you to backwards-incompatible changes to the way that Variables are implemented? If we could go in there and overhaul their APIs I think that might make #1102 be better. Not exactly sure what I'm looking for yet.

I'm thinking of if someone has gone and subclassed Variable then this might break them.

[fgregg]

i'm open to big changes, but i doubt we need to make them breaking.