One of the things that really impresses me about Vim is how fantastic its split management system is. No other editor, imho, comes even close to what Vim offers in this area. Sublime Text’s split window management via views is absolutely horrible.
I’d love to see Atom provide the ability to split windows as easily as Vim provides. For instance, It would be nice to be able to right click (and have key bindings for this, as well) inside a window and be presented with options to split the window horizontally and vertically. In addition, right clicking on a file in the tree view should also present these option but use the context of the last window that had focus before right clicking on a tree item.
Also of importance is the ability to navigate between splits, such as with Vim’s CTRL-W CTRL-W. Even more awesome would be to show a number (starting at 0, for instance) when pressing CTRL-W CTRL-A above each window, and then take a number inputted by the user to match one of the windows and navigate to that window by giving it the focus (this isn’t a Vim feature but rather a tmux feature that would be awesome to have).
If this were implemented then Vim emulation could build upon that to remap key bindings for CTRL-S, CTRL-V, etc.