It wasn't clear to me from the paper whether this is meant to
replace the JSON Compilation Database (compile_commands.json).
There is some mentioning of it but I couldn't understand what
it all means.

In any case, if the answer is "yes" or even "sometimes", then
I think this effort is overlooking headers. Recently I've learned
that the compilation database is sometimes extended to include
headers (what it means to have a compilation command for a header
is usually unspecified). There is a long and still open issue
for CMake on this:

https://gitlab.kitware.com/cmake/cmake/-/issues/16285