I’m not as well-read in anthologies as I’d like, so forgive me if I suggest something that’s already been done (if not done half to death), but I came up with a few possible ideas based on what I’d write and want to read.
One I’ve had for a while: I could be wrong, but it seems the traditional “beauty and the beast” dynamic is the norm, so why not change it up? “Beauty is the Beast.” Straight pairings, or maybe a mix of straight/bi/lesbian. Either way, exploring love, intimacy, and/or steaming hot sex with larger, stronger gals, such as dragons, gryphons, werewolves, gnolls, and so on—I hesitate to say more ‘bestial’ or ‘monstrous’ species, but I hope you get the idea.
Or, more generally, just exploring human or anthro with quad/feral characters (passing the Harkness Test, of course). I do recall at least one anthology having done that in part, but why not have more of a good thing?
Or! Slightly inspired by the XXXenophile suggestion, throw a biological wrench in the “Universal Male/Female Adapter” trope, whether it be different mating habits clashing or two rather different anatomies requiring creativity to get the best bang for the banging. Though now that I think about it, that might work better as part of a “trope-buster” anthology.
How can you go wrong with quality lesbian stories? This would work great, too.