What if Sketch stopped charging and went open source? Could a business possibly be built around services? Paid plans for Sketch cloud? Premium services for plugin developers? They already provide an open source file format. Sketch could swallow a lot more market share and essentially become the defacto design tool for everyone. Similar to what WordPress is to the CMS market.
This idea isn't meant to convey that Sketch is struggling. There is no incentive for the company to do this today. But in the near future it become harder to compete in a really crowded landscape. Seems like this path could position Sketch really well for the future that is to come.