I like this

This opens the opportunity to have different types of diagrams. It could be that we create separate ClassDiagram, SequenceDiagram, etc. types, instead of using the diagramType objects we currently use.

I think most digrams are fine, but sequence-like diagrams are difficult in Gaphor because they have a pretty defined layout and Gaphor provides too much flexibility in placing items for that particular diagram. A more structured foundation for them might be beneficial, maybe something structured like Eclipse/Capella in the future? This typing also enables tuning autolayout tools to the diagram type which can produce much better results.

I think most digrams are fine, but sequence-like diagrams are difficult in Gaphor because they have a pretty defined layout and Gaphor provides too much flexibility in placing items for that particular diagram. A more structured foundation for them might be beneficial, maybe something structured like Eclipse/Capella in the future? This typing also enables tuning autolayout tools to the diagram type which can produce much better results.

I did not even think of this. But yes, it opens up a lot of possibilities.