In database view, we use custom action statuses of "attended, spoke to, handwritten note sent, declined" in conjunction with the 'complete' date. We only use "closed" if nothing ever came of the action. The only action status NXT allows to be called "complete" is "CLOSED." If NXT could allow the final action statuses to map over from the database view, that would be fantastic. Because NXT doesn't allow this right now, we have thousands of actions that ARE complete in database view that are marked "incomplete" and "overdue" in NXT web view.
I think you can actually do this already (if I understand you correctly)- OPen a constituent in NXT web view. Scroll down to Action and click on the cog icon to look at settings. if you then choose "Use Action Status codes" it allows you to choose which ones will automatically close the action when you select it and which ones won't.
Hope that helps