It would be easy to add. The data in the drop-down list of values mainly comes from the NLS locale info, but the BINARY and BINARY_CI are explicitly seeded. Perhaps this was originally coded prior to the availability of accent insensitive sorting capability.
For the time-being, you could add the ALTER SESSION command in a login script, and set your preferences to start-up each connection with it:
Tools > Preferences... > Database > Filename for connection startup script
SQL Developer Team