As we have found from this thread, EN is not interested in this issue. It's quite ridiculous, IMO, that they would not incorporate this very basic feature into their product.
Anyway, as scttdb mentioned (page 8), it is possible to install the set of OS X Services very kindly made available by Devon Technologies for managing text. As an alternative, for those who prefer to "roll their own", I suggest a simple Automator action be created:
1) Launch Automator, create a new Service, and tell it to get text (from any app) and allow the action to replace that text
2) send the text to a shell script and invoke the "sort" command
3) save the action as a Service and you're done!
Then simply right-click on a selected section of text and select your new Service action. It works well for me, although <caveat emptor!> it will strip your lists of checkboxes, etc, so I advise the use of this on plain lists of items only. Still, it's effective and simple, and the great thing is it allows you to use your action in any other text app on your Mac as well!
For in-depth instructions, please go to Mac OS Automation's excellent article on creating a sorting service in OS X.
Also, much thanks to frank.dg "The Mischief Maker" for suggesting WorkFlowy. I am going to enjoy using that in the future!