I've been hoping to see this feature added via plug-in since I was introduced to Sublime, but apparently one can not create sidebars via plugin. This is the only reason I still use netbeans when I'm digging into code that's new to me.
I've already bought a license so it won't be the feature that gets me to pay, but I could count a few employees here at the office that would switch if it had this ( plus go-to-symbol which is coming in ST3).
Even if we just get the ability to add our own sidebars via plugin that would be great. I'd either write it myself, or pay someone to write it.