It'd be nice if you could provide an estimate in an email...like the invoice...to a customer a the start of a project or before the start. And then, once a project is working, if you were able to create and send an email with a change order quote when a request is made outside of the scope...that then would track their acceptance of this.
Perhaps it's asking a lot, but you've built such a nice system...I just want it to do everything.