Hot take: ABI stability is overrated. How often do you need to relink specifically without recompiling everything? As an OS packager, it's no big deal to rebuild everything depending on a C++ shared library when that library is updated. For self-contained binary distributions, statically linking the C++ library or putting the shared objects together works fine still.

vtables are always a pain, but I think the Swift team had some cool ideas about vtables and other dynamic stuff across dynamically linked shared objects..

upd: https://gankra.github.io/blah/swift-abi/ this