I would think of them as two separate questions:
- who can edit a wiki post?
- who can make a post a wiki?
“self wiki” never comes up for me, I generally set posts to be wiki by default at the category level.
Sometimes you don’t want a wiki, you want a message that will become stable as the edit grace period, because that’s important for consistent conversation (the main thing Discourse is going for). Having lower trust levels turn any conversation into a wiki, even in categories where it doesn’t make sense could cause confusion… but you are probably okay with having it lower.
You definitely want
min trust to edit wiki post to be low if you want more people to edit them. TL1 is fine for that.