Those ears are very cute. Simple but reasonably-priced, just the way I like it. xD I've seen cat ears one or two other places I can't recall right now, too... hmm, I'll have to see if I can dig them up. Will post them if I do.
I agree, Trethowan. I think they'd do very well. Silverbeam, whom I should probably
link for those unfamiliar, does a little of that, 3D printed. Wish they'd do more, their work is pretty cool, but it is again limited to mostly horns as far as option parts go.
edit: Looks like
this person has, in addition to horns (some tentacle horns, which I love xD), a pair of
hooves for Delf boys type 3 and 4. By the artist's own admission the cast needs work, and they're expensive as it is, but this shows promise for sure! I hope they keep working at it because I have a very powerful need for some unicorn BJDs.
edit: Some rather cute horns
here, pictured on MSDs, Monster High, and others! I have
got to get a set of those octopus arms. Or ten.