[zozbot234]

"Strong C++ interop" can also be achieved via libraries from an existing language, as with the Rust "crates" cxx, autocxx, crubit. So the jury is still out as to whether an entirely different language, namely Carbon, will be useful. OTOH, cppfront can be seamlessly transpiled to C++ on a file-by-file basis which can also be a desirable feature wrt. incremental adoption.

[HALtheWise]

My understanding is that none of those crates support both instantiating C++ templates from Rust and instantiating Rust generic functions from C++, let alone stuff like implementing a Rust trait with a C++ object from C++ code. These things would be _very_ difficult to do because of the impedance mismatch between the languages, and so there's space for a language with "even stronger" interop.