I have a feeling Shamrock now has Saturn's devil fruit power. The mechanics of Saturn's telekinesis it whatever were explicitly shown and never explained so it's definitely making a comeback.
Maybe Imu's abyss powers are related to how Blackbeard got the Quake fruit power.

I don't know why Catarina De Von wanted to imitate Saturn. Maybe Saturn's termination isn't public with the marines yet and Blackbeard will use her to impersonate a buster call.