Note that the thread you link to is a situation where they took an entirely closed source product, CodeCov, and made it source available under BUSL (and now FSL).
> Unlike other companies, such as Hashicorp, who admit that their software is no longer open source Sentry wants to have their cake and eat it too.
From the parent article (FSL: A License for the Bazaar, Not the Cathedral):
> But one thing is clear: until its expiration, the license does not qualify as Open Source. While I recognize the sensitivity around the term “Open Source”, I assert that the FSL's approach is more closely aligned with Open Source ideals than mere source availability. I consider it an “Eventually Open Source” license, though perhaps a more fitting term needs to be found.