No, in BProc custom elements are not implemented. However, there are mechanisms that you can use instead.
For example, for service task, when you select a Spring bean from dropdown list, UI elements to edit service methods parameters are displayed - you can configure service task there. See description and screenshots the Spring Bean Service Task section of the documentation.
When you select a JavaDelegate service task, then UI controls for managing JavaDelegate fields are displayed.
So you can view and configure properties that have “business” names.
For user tasks, if you need to do a custom assignment, you can do it using the UserProvider. Another option is to use predefined task listeners, that may do an assignment or whatever you want when the task is assigned or completed. We don’t have a separate documentation for it, but you can get an idea from Flowable documentation.
We keep an idea of “custom elements” in mind but don’t have specific plans for its implementation yet.