I'm using 2016a. I'm aware of the help article you are referring to. It mentions that Matlab tab completion helps with completing file names, which is true -- but only for certain functions, like save() and load(). I'd like tab completion to offer filenames whenever I start typing a string, not just in the few functions it is explicitly enabled for.
Here's some documentation about how to enable tab completion for additional functions, but this looks very tedious. Also, this method doesn't allow enabling it for all strings, irrespective of whether they are function arguments or just variables: http://undocumentedmatlab.com/blog/setting-desktop-tab-completions
