I don't work for Stack Exchange (I'm just a volunteer), but I can pretty much guarantee you that this feature will never be implemented. There are several good reasons for this, probably the most important is remaining a level of uniformity across SE sites.
If you want this you'll have to do this client-side. I believe there are several projects to create a "Vim-like textarea"; all you need to do is make a user script or extension to use it everywhere on the site.
Note that we already have a vi-se GitHub repo. Ping me if you (or anyone else) is interested in working on this and I'll make a new repo.