I'm speculating, but I think that if one enforced "module is a namespace", projects like Qt, standard libraries, and other libraries would be forced to ignore them for far longer than anyone wants due to ABI stability requirements. If `#include <vector>` got you a different `std::vector` than `import std;`, I don't know how you would get everything that passes a vector over an API boundary ported without doing it all-at-once.

Not to mention that if it were the case, things like a "Boost incubator" library would be in a separate top-level namespace as it could not "inject" itself into `import boost;`.