I don't think it's really that different. Elastic did that same thing about three years ago when they made all of their enterprise-only features source-available (https://www.elastic.co/blog/doubling-down-on-open). Timescale also made their enterprise features free of charge, but that's a business decision rather than a question of licensing. It's because their revenue model is based completely on their managed cloud offering while Elastic still gets non-trivial revenue from selling their enterprise features to customers who want them.