As suggested, I’ve submitted a feature requested. However, I feel the latest version of the BucketIterator of torchtext might be already sufficient. At least, I saw some examples online where it was used for machine translation tasks. While it “only” minimizes the padding, one can argue that this hardly effects the accuracy of the model anymore. I haven’t checked the inner workings of the BucketIterator, though.
EDIT: Link to the feature request 48 in case someone wants to comment on.