Hello! So recently, I often reply to comments and then it starts to get too deep. When this happens I end up having to go into the source editor and add the outdent template to the start of my reply (possibly with the parameter with the number of colons, depending on how deep it got). Maybe this could be integrated into the reply tool, with a button allowing you to outdent your reply, optionally with the parameter of the number of colons. I don't have a mockup of how I think this would look like (i'm not an artist and never intend on becoming one) so hopefully I'm able to get my point across like this.
Topic on Talk:Talk pages project/Replying/Flow
Auto-outdent-template seems a reasonably uncontroversion automation. When it gets too deep, the reply tool could automatically insert an outdent template. We'd just need to decide on the wrap threshold.
I always outdent once posts exceed eight indentations deep. Eight indentations, in my experience, is the maximum indentation level where comments are still fairly easy to read on mobile.
+1 for outdent feature too.
In addition to the need for an outdent feature, using the outdent template used at English Wikipedia appears to break the ability to use the "Reply" feature.