Version 0.6.4-1 of powerlevel9k is marked for autoremoval from testing on Mon 02 Jul 2018. It depends (transitively) on powerline, affected by #899135. You should try to prevent the removal by fixing these RC bugs.
Last update: 2018-05-27
Standards version of the package is outdated.
The package should be updated to follow the last version of Debian Policy
(Standards-Version 4.1.4 instead of