One potential issue would be that the compiler is free to assume any type with the name `foobar_t` is _the_ `foobar_t` from the standard (if one is added), it d

One potential issue would be that the compiler is free to assume any type with the name `foobar_t` is _the_ `foobar_t` from the standard (if one is added), it doesn't matter where that definition comes from. It may then make incorrect assumptions or optimizations based on specific logic about that type which end up breaking your code.