> It turns out that the Itanium and Microsoft ABI's don't have this info inside their type_info, and so I'm not asking for it anymore.

And here's my problem. If you had a good reason to make this change to begin with, why would it matter that "Microsoft ABI's" doesn't have this information?
The priorities here are reversed. You had something and went in search of a reason. But what you should do is have a reason first, and then look for a solution.