Here follows an unordered list of things to be implemented:
The GMFMap model allows to initialize created nodes in the diagram with some content as specified by a ElementInitializer rule. It would be nice to have this opportunity also with GenGMF.
This feature has been introduced in GMF 2.3 (Bug 138179) and is missing in GenGMF. It allows to show and edit multiple features in one label.
This feature is useful for GenGMF to provide some basic Templates as part of the distribution. Wizards can be used to copy them into the own GenGMF model. On the other hand you can use it to create your own TemplateLibrary.
Please leave a comment if you are missing a feature!