When is the Earliest Possible End of Service Date for Project Server Subscription Edition?

Great points Rob, and I think the article I mentioned was forced on Microsoft by some large customers who had a huge investment in SharePoint and/or Exchange, and couldn't run their businesses on a "12 months' notice" solution. I think the biggest risk of just using it "out of support" is if some change to the Project client's file handling broke connectivity to the server - and Microsoft just held their hands up saying "out of support".  Of course, you could just avoid patching the client, but that sort of break has in the past come from security fixes.