So let's require C11. I understand systems stuck on C89; we don't support those anymore. I feel like being stuck on C99 and not being able to use C11 would be much rarer. Besides: C99 compilers usually supported anonymous structs and unions as an extension. GCC, for example, supported anonymous structs and unions back in 2002, at version 3.2.
Can you think of a *real* situation where someone would be inconvenienced by our relying on this feature? Avoiding it feels like conformance for conformance's sake alone.
Sure. Ideally, we'd have accessors for more things.