Maybe I missed a step, but I can only put one main so far. I haven't seen anyone posting secondaries. Maybe the feature can just be implemented by making it "main characters"?
The secondary character feature was never implemented. You can only list your primary character.
On a side note, I can't see "main" and IDs/gamer tags/friend codes when I click on a person's name to see their profile. I have to look for their posts, manually, to get this info. Is it purposely set up this way?
You can't see any of that info on their member card thing (the window that pops up when you click their profile), but you can see it on their actual profile page. On their profile page, you'll see the tabs "Profile Posts", "Recenty Activity", "Postings", "Information", and "Recent Media". Click on "Information" to see their main character, XBL Gamertag, PSN ID, et cetera.
Also, note to admins; in the list of available options for the main character setting, all of the characters who have known last names are listed with their first and last name (like Helena Douglas, Tina Armstrong, and so on), yet Bass is just "Bass" instead of "Bass Armstrong" and Lisa is just "Lisa" instead of "Lisa Hamilton".
Also, the only characters with aliases that have their aliases as options are Bass/Mr. Strong and Lisa/La Mariposa. OMEGA doesn't have a "Genra" option and Tengu doesn't have a "Gohyakumine Bankotsubo" (or at least just "Bankotsubo") option.