I would prefer a non-modal dialog window, so you can change the selected objects on the map without having to close the window.
Some images for the buttons are always nice.
When testing the features, I noticed, that you cannot undo the actions made by the plugin. This is a serious problem - JOSM does not support direct change of the primitives in a Dataset. Instead, all modifications have to be send as Command objects via Main.main.undoRedo.add(…).
It’s a little surprising that the ‘Building generalization’ button operates on the entire Dataset and not just the current selection. This could lead to interesting results when a novice user aligns an entire city and uploads the results…
I don’t know anything about CAD, but is ‘Building generalization’ a good description for what this feature does? From the name, I would have expected that it simplifies the shape of buildings or something like that. Instead it aligns buildings to the nearest road.
The ellipse feature is quite nice, I will use it for sport stadiums!