The Zulus were the guys pushing the hardest for a federal model for a post-apartheid South Africa, and in the 1980s, there were serious suggestions of creating a Swiss-inspired canton model for South Africa.
I personally don't know if federalising the country into ethnic based states would have been such a good idea. South Africa has probably been one of the African countries most successful at creating a common nationhood, a "South Africanism" and I think this could have been undermined by ethnic based sub-national divisions.
Although the ANC is Xhosa dominated, alot of the top officials are not Xhosas. Zuma is a Zulu for example. The ANC always made one of its principles that it was a party for all South Africans, not just Xhosas, or blacks, or whatever the case may be. That is also why you see this infighting in the party, with leftists vs social demcrats vs liberals vs Zulus vs Sothos vs Marxists etc. The ANC is actually a broad political church.
Back to ethnicity in the country, most South Africans are proud of their ethnic heritage, but I think you'll find many will descrivbe themselves as South African first, and then only as a Zulu, Pedi, Venda, Afrikaner, Indian etc.