Zanda isn’t a political rival because she’s been in exile for years now iirc. If she got with T’Challa (FWB or otherwise) it’s as a rogue princess turned archaeologist, not a head of state with a political agenda at odds with his own.
And speaking of archaeology, with the recent reveal that Sue’s doctorate is in that field I’d love an arc where T’Challa and the Fantastic Four fight the Collectors or something. Zanda should still be a member of the group so it’d be fun to see her dynamic with Sue and other longtime allies. Zanda has potential as a love interest, she’d push T’Challa and the franchise in a fun new direction if they capture her personality well.