I think they're understating the thread safety risks here. The import is going to wind up happening at a random nondeterministic time, in who knows what thread holding who knows what locks (aside from the importer lock).
Previously, if you had some thread hazardous code at module import time, it was highly likely to only run during the single threaded process startup phase, so it was likely harmless. Lazy loading is going to unearth these errors in the most inconvenient way (as Heisenbugs)
(Function level import can trigger this as well, but the top of a function is at least a slightly more deterministic place for imports to happen, and an explicit line of syntax triggering the import/bug)
Previously, if you had some thread hazardous code at module import time, it was highly likely to only run during the single threaded process startup phase, so it was likely harmless. Lazy loading is going to unearth these errors in the most inconvenient way (as Heisenbugs)
(Function level import can trigger this as well, but the top of a function is at least a slightly more deterministic place for imports to happen, and an explicit line of syntax triggering the import/bug)