As someone who hasn't watched Classic Who aside from a handful of episodes, I had little idea of who Omega or The Master were prior to TEOT and Utopia. I know who Susan is but not much about her, and I've heard the name Rani before (So Master is Darth Vader and Rani is Tarkin/Thrawn?) but I'm not familiar otherwise.
I also don't really care for the Bigeneration schtick, although if it's used well I can live with it. I don't see how the Doctor and Susan can fight 2 Rani, 2 Omega and 2 Masters so I'm wondering if another Doctor will return.
Personally, I'm hoping this season will end the 'magic' started in WBY and dispense with "Mavity" and Gods and Bigenerations etc.