@Gargron I am new here but my online roots go back to running a Wildcat! BBS starting in the late 80's.
You made the right decision to not allow QT's and I hope you stick with it. Opt in just seems like it would be a mess.
I just read this whole thread and without any QT's it just flowed in a relatively focused way. I like Mastodon for this.
Would QT's increase the moderation burden on Instance Admins? That would be bad.
How many levels would be allowed? Could I QT a QT of a QT of a QT?