Hi there!
We decided to develop a SyliusInvoicingPlugin and from what I observed, there’s quite a lot of interest in it. Invoicing is a tricky part of any eCommerce and it highly depends on your local law. We are not able to create something generic on our own, as we are not aware of all factors of it.
So far, it’s going to be fully legal in France and Poland, but I am sure there are more aspects that needs to be covered.
Help us on https://github.com/BitBagCommerce/SyliusInvoicingPlugin 
Nice work guys! I’d recommend adding some admin/invoice screenshots to the README. Before we launch the Sylius Store. 
I think that it would be worth to prepare a README plugin framework for the community. We don’t even have a standard yet. I think this might make the plugins even more useful and will prevent people from reinventing the wheel as from what I can see now, many folks just give up plugin installation, just because have no clue how they do work. They decide to work on their internal ones from scratch.