1 team functionality with multiple user accounts
2 easy to use workflow for double annotation where each text is annotated by exactly two annotators. The software should make sure that a text is never shown to more than 2 annotators and never shown to the same annotator twice
3 make it easy to review the 2 versions and solve conflicts
4 smarter alternative to review would be a warning system that identifies annotations that may have errors (because a model trained on the other data predicts a different result) and automatically flags it for review by another annotator
5 stats on the annotators: speed, accuracy, statistics on how frequently they assign different labels to detect potential misunderstandings of the annotation schema
6 GUI with overview of all annotation datasets, with stats like % finished annotating (with stages for double annotation and review), the types of annotation done, frequencies of labels to detect imbalances
7 functions to mass-edit the annotations, like renaming or removing an entity type
Another thing I'd be interested in is some integration with a third party annotation provider. There are companies that offer annotation as a service and it's also available on Google Cloud and AWS. Having that integrated into an annotation tool would make it very easy to get large amounts of well annotated training material.