TL3 users can definitely opt into wiki on their posts, I have done it a few times, but it seems if you don’t do it soon enough after you create a post or topic the ability to opt into wiki expires with the ability to edit.
EDIT: Huh, I just went back and checked the BBS Style topic, a wiki I created a little while back (I’m sure you remember it ), and it seems the ability for me to remove the wiki has expired as well… is that supposed to happen as well?
EDIT 2: @M_Dub you should hit up @beschizza, @Falcor, or @codinghorror to reopen your topic to editing, or being wikied.