Is there a reason (except for someone has to implement this) why collapsed event-subprocesses are not supported? There is not even an icon bpmn-icon-event-subprocess-collapsed.
I assume that the possibility to collapse event-subprocesses could use the same infrastructure as regular subprocesses. Or in other words, can 'shape.toggleCollapse' be fired for event-subprocesses?
Also, the modeller is able to show collapsed event subprocesses which are created with other tools (Signavio). The only problem is that the trigger is not displayed as described on p. 388 of the spec, but that is relatively minor compared to not being able to collapse/expand event subprocesses.