That is just like, your opinion man 
I can see multiple use cases:
- Q&A archetype, Question remains normal, some answers are wiki.
- Topic summary post for long topics, such as Underrated and overrated films (and other general filmy chat) - general topics - Boing Boing BBS which would be totally fine as post #2
- Full Wiki topics, where post #1 is a table of contents and rest of posts are linked from there
Etc.
Admins can do whatever they will, then can rewrite posts, impersonate users and wreak havoc with a forum if they wish. It is the nature of being an admin. Besides history is not going to be rewritten as part of un-wiki if ever needed so you can track it down. (Though admins will need nuke revision at some point)
There is a VERY important order of operations here. This is a strategic feature that we need first before building a huge battleship. This is a small, well specified, very useful feature that could be implemented in days. And must happen before we will even consider merging a wiki archetype into core. (which must be will specified regardless)