The SQLite comparison someone mentioned is spot-on. SQLite has kept TH3 (their 100% branch coverage test suite) proprietary for years as a monetization strategy, and nobody bats an eye.

Whether tldraw's issue was a joke or not, it highlights a real tension: open source maintainers are watching AI companies train on their code, tests, and documentation - the very artifacts that make software reliable - and then use it to generate competing implementations. Tests are arguably more valuable than the code itself because they encode the specification and edge cases.

I suspect we'll see more projects adopt a split model: open source the runtime, keep the validation suite proprietary. It's a natural response when your test suite becomes a training signal for competitors.