uint32_t is in the standard since C99. But it is conditionally present - it's only there if the platform can provide it. In practice, all platforms that most software cares about do so. But it's not actually codified everywhere, and that codification is what I was talking about.

uint32_t is already available on the platforms where it makes sense to support the type. It is a strength of the C language that it also supports exotic platforms.

By 'standard' do you just mean more widespread use? Some APIs already do something like this, such as Windows with its 'DWORD'.