Sounds like something that should be part of a theme to me.
If you wanted to make such a theme, in-place editing isn't really difficult, you're just swapping visibility between a text block and a text input. Client-side you would only do the swap for the correct user(s), and then server-side verify and actually change the topic title.
A few weeks ago we weren't checking the slug for correctness. So https://community.nodebb.org/topic/2647/anythinghere was working. But if you had images in the topic in the form of !(/no/url) this was causing an api call to the topic and loading the entire topic to solve that we started checking the slug.
If we can find a solution to that image problem we can go back to ignoring the slug.