Right, I'd forgotten about the solving engine. Is that licenseable? I mean, it may not be worth while, any time soon, especially if it's an expensive license, but that seems like it might help; integration coding is probably easier than writing the core from scratch.

Having a more robust history and having it available programatically would be great. Honestly, it'd be nice to have it explicitly represented in the UI, too -- if you had an available, editable history, that might actually do a lot of the same work you'd lean on a constraint system for, at least in the trivial cases.

/Ella