Looks like they went full Amazon, by forbidding developers to work in OSS side projects. I cannot really believe it's that no politics talk only: https://news.ycombinator.com/item?id=26944192
There's no way that Basecamp forbade developers from working on Rails related side projects. A good chunk of what Sam Stephenson has worked on recently has been instrumental to launching Hey, and Basecamp has long benefited from their association with Rails and influence over it.