Right, an animated kissing scene is definetely not an easy thing to do. Characters heads are quite close together, which can easily lead to clipping issues if you are not careful. And even worse, the missing rigs on the tongues make it so much harder to put everything in motion and at the same time let it look natural.
If I remember correctly I have done one lesbian kissing animation so far. Overall it's just a small part of a very complex animation (crazy tentacle scene with a lot of stuff happen at once).
Here are two close-up shots of the kissing scene, if someone wants to see (be aware of the audio):
For what it is, I think it came out quite good, but I would also like to have more options on hand to go even further. Rigs were already used to their limits.