I've just had a game in which i attacked form the south of shaka with cavalry and the north with redcoats. And the cavalry did most of the city taking!
so i am forced to conclude that Cavalry rush isn't dead.

Was Shaka defending with Rifles?

I was thinking about using a Charismatic Civ that produced 13XP Cavalry (Barracks + Stables + Westpoint + Civics or GGs) and rush with Cavalry and Spies for a quick attack, the Spies would revolt city and eliminate cultural defense, while my flanking Cavalry would weaken any tough defenders and my combat 4 or combat 3 pinch/blitz Cavalry would finish them off.