I recommend following the answer from @Tyler because it encourages using org-mode as designed.
However, if you're absolutely determined to archive a list item then:
- Place point on list item
- Move list item to bottom of the list using M-down.
- Convert list item to heading using C-c *.
- Archive header using C-cC-xC-a
This should leave the original file that appears similar to this:
- plain text
- even more plain text
and create an entry in archive file that is similar to this:
* more plain text
:ARCHIVE_TIME: 2016-11-16 Wed 11:27
Note: If you have any content under the header after your list do not archive or you'll archive more than you want too. This method only works on very simple use cases such as your example.
Hope that helped!
This answer was tested using
GNU Emacs 24.5.1 (x86_64-unknown-cygwin, GTK+ Version 3.14.13)
org-mode version: 9.0