We just had a user report a wish item in bugs.kde.org asking for Okular to come with a text strike-out annotation by default. I just closed the bug saying that he can create his own annotations by Settings -> Configure Okular -> Annotations -> Add ->
Text Markup -> Strike Out -> Set Color -> OK
Of course we could still ship it, but if you have a look at that "Add Annotations" dialogs there's lots of lots of possibilities so people should just create the ones they see the need for instead of us shipping lots that may not be that useful.