The requested feature is available in the latest HelpDesk version (2.1.25). You can set as default either a current status or a specific one. In the latter case, you need to specify the internal name of the status in lower case with spaces if there are any. To set the default status, edit the ticket form and set a ‘default-status’ attribute of a ‘save-as’ element.
<save-as default-status="current"/>
or
<save-as default-status="in progress"/>
