"Breaking ABI" isn't an issue unless you can't compile your code anymore. It's pathetic that C++ has been so hamstrung over ABI that we're willing to stop improving.
GNURadio consistently uses pimpl for blocks, as I understand it mainly for ABI.
> willing to stop improving.
I think that dismissing it like that shows a naive understanding of execution environments, binary interface design, and in general systems software engineering.
If you want the latest and greatest, a willingness to rebuild your code seems like a reasonable prerequisite to me.
If you need a binary blob that can withstand toolchain versioning, use a dynamically linked library.
So regardless of what WG14 and WG21 do, compiler vendors will ignore them, if it means angry customers.
In design by committee languages, new standards are only relevant to the extent implementers actually care about them.