you just know a company like Microsoft or Apple will eventually try suing an open source project over AI code that’s “too similar” to their proprietary code.

Doubt it. The incentives don't align. They benefit from open source much more than are threatened by it. Even that "embrace, extent, extinguish" idea comes from different times and it's likely less profitable than the vendor lock-in and other modern practices that are actually in place today. Even the copyright argument is something that could easily backfire if they just throw it in a case, because of all this questionable AI training.