That's not quite true. That's already possible without a standard ABI.
What's not possible is to get code compiled by a specific compiler to call modules built by another compiler provided by another vendor. That's the only problem that is addressed by a common ABI.
I would also add that considering MS's interoperability history and how prevalent MSVC++ is, working on a standard ABI would be a waste of time.
Yes, compilers need to agree on the ABI, the platform ABI, that is. Today most platforms already have a de-facto or de-jure standard ABI and compilers have the option to implement it.
Even if such a thing was possible, there is no value in the standard committee standardizing an single ABI as most platforms would never break backward compatibility to switch to it.
ABI is ancient since it defines the underlying structure that allows you to link compiled object files and liberals together (the latter both statically and dynamically). Allowing code generated in one module to successfully call functions in another.