A spell checker is pretty useless. It's not a word processor. I just want to very quickly open a text file and perhaps make a small edit. I would usually use it for config files.

Syntax highlighting for xml, JSON, yaml and CSV would be a much more useful feature. gEdit on gnome really nails the lightweight but useable text editor.

Also, would it kill them to use a rolling buffer instead of loading and rendering an entire 500MB file before rendering the first 30 lines on screen?

People say "just use [editor]", but it's no good when you're configuring someone else's prod environment 7 proxies deep, and all you can use is notepad.