If OSRF were to do that, there would be a fork. All those companies and research labs deeply invested in ROS wouldn’t just say “well, it’s been fun, I guess we’re just going to do something else now”. Everything necessary to run one’s own build farm is open source, so it’s not like OSRF have a kill switch for ROS in their hands that they can push at any time. But probably there wouldn’t be just one, but multiple forks; also, without a source of funding, it’s unclear to me how the fork would be able to keep up the quality of support that OSRF is providing at the moment. Thus the “chaos, confusion and pain” I mentioned in my earlier post.
That said, I have confidence in OSRF to do The Right Thing™ (i.e., not trying to actively kill ROS), and I really believe Brian when he’s saying they’re not a gang of super villains. 
Your points about the shim are very good. I get the same vibe that it’s not going to happen, but I still believe we would really need one for the reasons that @ooeygui listed. 