This really needs to get solved. 

It's pretty clear that QB didn't think through this use case very well.

No business owner has the time to go creating a separate projects form before the prospect has actually paid at least a deposit on their invoice and become a client.

If anything there should be a checkbox when creating an invoice to automatically create an associated "Project"  and workflow once a partial or full payment has been recorded from the customer.  We should be able to create custom workflows inside the "Projects" based on the line items inside the project. All to happen automatically when the customer pays. 

For example, "Ordering parts" associated with a line item on the invoice. With clickable contact information and links to the vendor or sub-contractor. This way we could truly create and manage projects and put a monkey in front of the computer to help carry our the tasks. 

I don't want to have to train an employee to know that every time they see line item A that they now have to look up Vendor B and contractor C, but if they see  Line Item B then they need to email vendor C and order 27 color glossy photos. It would be sooo much easier if we could make that all happen automagically. ;-)

Which QB has the technology to do. They just need to do it.