That’s reasonable, but it’s also blowing the request here a bit out of proportion.
Let’s ignore the wiki aspect of this for a second though: at the core this feature request isn’t about wiki-functionality at all, it’s about post-editing.
Let’s say I write an announcement post in my forum about a release I do, and it’s just a long post by its nature. It’s not a wiki post at all, just a really really big post, with multiple headings.
The idea described here would make that much easier to work with, and Discourse supports the creation of that kind of post in the first place. Why is it a bad idea for Discourse to not support easier editing of such a post?