For data files, would be great to be able to sort page content and remove duplicate lines
Not sure whether this really needs to be done by a plugin. E.g. you could use send selection to in combination with sort |-u]
Exactly. Using 'Send selection to' can be used for this, I do this since years. Attached is a screenshot of my configured commands, the first both do exactly what you want. Easily accessable using Ctrl-1 and Ctrl-2.