Diageo fucked up
you have to the always think about licenses when accessing an SAP system. many customers have this kind of "cheating" ideas but you always have to ask them to think a little before they spend a couple of millions developing in the wrong direction. You're using services on the SAP system it's not a stupid database so you're executing business code on SAP. They paid for named users not technical and I bet they were using technical users to access the data (because it's typical).
It's not that hard to move to a different system - I see companies do that all the time.
I have a nagging feeling that Diageo bought first SAP and then another executive came who pushed for Salesforce. And Salesforce by itself was not enough and still had to get SAP data so they built a connection to it. It might be a board-level fuck-up or political.
Truth is SAP is extendable in function and storage to unbelievable heights. That's why it can be made to fit any company. So the more you extend, the harder is to leave it because no new solution will cut it.
About any other (obscure) solution but SAP or Peoplesoft or Siebel: if you build a custom solution and it's only known by one or two experts - you'll end up 20 years later bringing back people from retirement and not understanding the solution anymore - I've seen it too often! Not to mention that the custom solution will get staler and staler every year.
anonymous for obvious reasons.