It would be great if you could individualize an assignment with more versatility than at present.
For example, if I want to make a timed quiz, and I have students with extended time (pretty common with any kid with an IEP), I currently have to make two of the same quiz and assign each to a different grading group in order to differentiate their time. It would be great if I only had to make one quiz but could differentiate certain options (ie, time to complete, date due) to certain members or grading groups.
Moodle has this kind of functionality. And as it is open-source, you could look into its code to see how it does that.