@Paul Volk
This is a great question, and for some people these things can make a huge difference.
I actually have a system that does exactly this. Problem is - it's not available in your market and/or without a boots on the ground approach with it. Use it on every project, personal and business.
You can do exactly what you are talking about, but you have to do it piece meal and you can use something like DocuSign. Sure, it's a little more difficult, but you can make it work. Updating an electronic scope of work would have to be some sort of a shared document somewhere in cyberspace. You can do it - get creative with it. Hopefully your contractor or whoever you work with is knowledgeable, reliable, and will use your system. At the end of the day, your systems are only as good as the people using them, (or not using them).
We developed our own. Wrote our own code, etc. So ours is very specific to our needs. You can pull something together that meets your own specs.
Just like you guys, I am really interested to hear what others are doing to bridge some of these issues.