The A350-900ULR is already in the pipeline, hopefully (data has been submitted).
A330-300F as well, iirc.
321LR would go nicely with the 321XLR, wouldn't it?
A310-200/300F, I don't know.
@Simon: yes, but some markets could use it. Sure, it's a niche aircraft, like the 737-700LR, but still interesting.