Only in certain limited cases, for example, can't have static class instances or anything else that could require calling before a call from "extern C" API.
Also now you have to build enough of a C API to expose the features, extra annoying when you want the API to be fast so it better not involve extra level of indirections through marshalling (hello, KDE SMOKE)
At some point you're either dealing with limited non-C++ API, or you might find yourself doing a lot of the work twice.
