After I did some more research, I reformulate the question like this: is it possible to use a task template also for a milestone instead of the default milestone shape? If yes, how?
answered on 03 Jul 2017, 07:52 AM
The milestone has a different rendering than that of the task and does not support templates, whereas within the task the template is rendered as a specific div element with class "k-task-template", which in turn wraps the template's content. Currently templates are supported only for tasks.