Feature: Ability to see how Special:Homepage renders for different users.
Since the homepage is private, we can't have undocumented URL parameters like we often use to test features before they become public. Any on-wiki way to do this would require at least a new right assigned to a restricted group.
Here are the things we would like to be able to do in order to test the homepage.
Most of the modules on the homepage contain information that are specific to each user. The impact module shows the pageviews around their edits, the mentorship module shows them the name of their assigned mentor, etc. We want to be able to make sure that the content shown for different users is appropriately tailored to them.
Therefore, it would be best if it were possible for us to see what the homepage would look like for any given user so that we can test a variety of users with different sorts of welcome survey responses and edit histories. A URL parameter would be good. I can also imagine a text box on the homepage where we can type a username.
One thing worth mentioning is that nothing we'll be showing on the homepage is secret or personally identifying.