Now, the other interesting bit is that the project also has a Contributor Licence Agreement (CLA) which also seems to provide all copyright to Shopify. I don't really understand how these legal stuff work in software, but I heard that CLAs have been used in the past to profit off contributors by moving to another proprietary licence (MongoDB and Elastisearch did that)
Then do you (developers on HN) stay away from CLAs? It doesn't sound too risky for me, and I've probably listened to one too many open source activists.
Another question, if I may, would it be possible to relicense a fork of Polaris to MIT (removing the Shopify clause?)