Add the option to do a right click on nodes in the data inspector of each render window to open a context menu similar to the one in the data manager. Since the current design of the DataNodeContextMenu is unsuited for the flexible needs of the multi widget selection (being hardwired to get the node selection from a fixed source, even though we need to be able to change the source depending on the current render window), the best approach should be to implement a new context menu specifically for this.
For this purpose, it would also make sense to go through the actions in the existing context menu and find out which ones could be easily reused, and which ones need to be newly implemented for this (leaving the existing ones remaining). At the moment, all of them are written to work with the current context menu, being supplied with a berry::IWorkbenchPartSite::Pointer from which the node selection is often gathered. Ralf proposed to instead avoid this inheritance and go with a design that uses QT slots to notify the actions if there are changes in the node selection.