Hello mattr,
May be, I misunderstand you, but since the N++ v6.5, this feature seems available !
Just select the menu option Settings - Preferences - Auto-Completion and check the option html/xml close tag
Then, for instance, as soon as you typed the closing > character of the form <p>, in a html file, it adds, automatically, the string </p>, with the cursor between the two tags, for typing text. Nice, isn’t it ?
Cheers,
guy038