So to be clear, if we purchased the pack that included the servo skull, we don't have access to it yet?  If not, will we get it before release, or not until after? anyone know?

No one knows as yet due to no info being released about them from the developers. I would guess that they will be purely cosmetic although i would like to see some form of boon for them to be used but only as long as "minions" use are not exclusive to the packs only. 

Will probably  be one of your retrue once that feature is unlocked at a later  date