How does enforcing profiles per-translation unit make any sense? Some of these guarantees can only be enforced if assumptions are made about data/references coming from other translation units.
C++ code involves numerous templates, and the definition of those templates is almost always in a header file that gets included into a translation unit. If a safety profile is enabled in one translation unit that includes a template, but is omitted from another translation unit that includes that same template... well what exactly gets compiled?
The rule in C++ is that it's okay to have multiple definitions of a declaration if each definition is identical. But if safety profiles exist, this can result in two identical definitions having different semantics.
There is currently no resolution to this issue.
Its a bit optimistic cause modules are still not really a viable option in my eyes, because you need proper support from the build systems, and notably cmake only has limited support for them right now.
The tooling is way better than it was 6 months ago though asin I can actually compile code in a non Visual Studio project using import std.
I will be extremely happy the day I no longer need to see a preprocessor directive outside of library code.