They have been requested, but not via this forum unless I've forgotten. My plan has been to not implement them. There are a few reasons:
- Of the ones I have seen, I'm personally not crazy about their effects.
- I don't have images for them.
- They would take quite a bit of effort to implement and test.
- They would have to be optional, since adding them unconditionally would break everything already played.
- It would be extra work to let people choose subsets.
All could be overcome, but I think it comes down to motivation.