> You can address a lot of the pain points by making an alternative, clean-looking "modern" syntax that, because it's actually the same language as C++, would have perfect interoperability.
> Show that in today's C++ guidance literature we already teach C++ programmers to make local variables const, and link to a few examples of such guidance (which will contain more details, including examples of problems that the advice avoids). That will start to make the case. If you can do that, feel free to open a "suggestion" issue about it!
That "C++ guidance literature" is called the Rust book. Const by default won.
Sounds like Herb Sutter's cpp2/cppfront: https://github.com/hsutter/cppfront