Would have loved to do the same and that's my plan eventually, too. Alas, no time for fixing right now. And as I've already noticed when migrating from JS to TS

Would have loved to do the same and that's my plan eventually, too. Alas, no time for fixing right now. And as I've already noticed when migrating from JS to TS or non-strict TS to strict TS, there's a whole lot of issues that require thought and investigation whether everything is fine from a nullable perspective. I have found quite a few issues, even outright bugs, but when there are more pressing issues than a few lingering NullReferenceExceptions that no customer has stumbled over in the past decade, then those get prioritized. At least new code is forced to deal with those warnings for now, which is much easier than fixing legacy code.