> If you cannot automatically annotate the code there is no point in trying as you can't do it manually.

How can you know this without a "viral" analysis that tells you how much annotation is needed, and where? Perhaps the code factors out all the low-level, "memory unsafe" hacks to its own module, and that can be feasibly annotated. It's just not something we can know in advance.

> Perhaps the code factors out all the low-level, "memory unsafe" hacks to its own module, and that can be feasibly annotated.

While it is theoretically not impossible for that scenario to occur, I'd say it sounds wildly unlikely for anything that can be descried as 'old' code.