We have inline comment editing, inline editing of questions on Area 51, and inline re-tagging.
Can we please have inline Question and Answer editing on the Stack Exchange sites?
This has been implemented using a GreaseMonkey Script. Try it out yourself. It's old, so I'm not sure if it will still work:
https://meta.stackexchange.com/questions/12851/greasemonkey-script-to-edit-questions-answers-inline
Please don't link to the Grease Monkey script that allows this.
=> Why? Some people may be interested in it, such as me.