How did you decide that bukkake always implies a female subject? 

Also, just because a word has a historical meaning doesn't mean that it can't ever mean anything else as culture develops. The word rap meant "to knock, as on a door" up until the late 70s for example. Would you deny the more modern use of the term? The English language has no board to regulate it, as French does with the L'Académie française, so you have no basis for defining what the word means. We have groups and documents that define the proper use of words like "you're" and "your", for example, but none such for words like bukkake. If it can be shown that it is used in a particular way, that is valid. My personal belief is that there is no need for the qualifier "gay", just as there is no need to call men having anal sex "gay anal sex", but that's really irrelevent. 

I think it is important to make clear the historical implications, but not to deny that we are currently creating and modifying language. Even the fact that we have taken the word bukkake, "splash", from Japan and created this very specific connotation of splashing not just anything, but specifically semen and specifically onto a person's face shows that this term is elastic and subject not to rules that we impose on it, but by the meaning that it has to the people who use it.