Regarding option #4, I'll remark that experience tends to suggest users don't consistently read the `NEWS.txt` file on upgrade, so option #4 will likely essentially mean "LWT has a correctness issue, but once it broke your data enough that you'll notice, you'll be able to dig the proper flag to fix it for next time". I guess it's better than nothing, of course, but I'll admit that defaulting to "opt-in correctness", especially for a feature (LWT) that exists uniquely to provide additional guarantees, is something I have a hard rallying behind.
But a performance regression is a regression, I'm not shrugging it off. Still, I feel we shouldn't leave LWT with a fairly serious known correctness bug and I frankly feel bad for "the project" that this has been known for so long without action, so I'm a bit biased in wanting to get it fixed asap. But maybe I'm overstating the urgency here, and maybe option #1 is a better way forward. -- Sylvain
