This was tested using 8.01 beta 4, it does not work for 8.0. To rename in 8.0, export pool from command line first, then do a factory reset from the GUI and continue at step B. After completing steps B-E, re-enter your settings from the GUI (do not restore config). This also applies if you have datasets, in which case you need to do 'zpool export -f poolname' from the command line.
A) From the GUI Storage -> View All Volumes -> Export (button next to pool name)
B) From console #9/command line, assuming original pool was called tank.
zpool import tank NEW-NAME
If you get an error saying the mountpoint doesn't exist, ignore it.
C) Do a zpool status -v and verify your pool has been renamed
D) Now do zpool export again
E) Go back to the GUI
Storage -> Volumes -> Auto Import Volume
That's it!