Sendaz
Comments like that is why we can't have nice things. If you are asking because you genuinely want to know and not because you just want to argue for arguments sake, this is my answer.
If you were a player at my table and came to me asking to get a tongue, eye, ear, or genital focus, I would turn the question tight back at you. How would your character go about enchanting those parts of him or herself?
I don't have a problem accepting that horns can easily be inscribed or marked with magically infused inlays or ink. As far as I am concerned, this is similar to tattoo magic in all the ways that really matter. The same could be said for actually tattooing your ear or even your johnson. How do you propose doing the same for your eyes or tongue, though?
In my opinion, it would be a trivial matter to use a piercing as the actual focus for your tongue, ear, or even genital examples. As stated above, I don't see the original example to be any different from a tattoo focus.
And If you're arguing just to argue, I'll just state in no uncertain terms that i find statements to the effect of "oh, but if you allow x, what's to say a player won't ask for y!?" to be inherently boring. We're playing a game designed around having fun set in a fictional world where magic and technology is capable of feats we can only dream of. So I'll let my imagination be my guiding principle and try to make allowances for player desires as much as possible, even when those situations go beyond or even contradict the RAW. Seems some people just can't wrap their heads around not following "The Rules" to the letter these days, which is fine by me as long as that opinion doesn't also come with an accompanying "But you're playing the game wrong!" if I don't necessarily agree.
This question was asked in the Gear section, not the Rules section. You want to argue the rules as written, take it to the appropriate forum and leave me out of it. I merely provided my opinion as I would apply it at my table.
And with that, I'm out, seeing as I've already provided my personal answer to the original question.