First off I should preface this by saying I cannot provide evidence of a clear goal that the SABC was attempting to achieve with Shaka Zulu as I have not watched the work and I haven't conducted much research into the SABC during this particular year. What I can provide however is some important political context for 1986 and some discussion of Apartheid attitudes toward Blacks. Together these might provide some insight and possible motives.

A large part of Apartheid (particularly Grand Apartheid which was in Vogue for the Securocrats controlling the executive branch of South Africa at the time) was the Bantustan or Homelands system. The Apartheid state argued that the Bantustans were supposed to act as homes of all blacks and provide places for them govern themselves and engage in their own economies such as farming. In reality it was impossible to fit around 80% of the population on around 11% of the land of South Africa and this was often the worst land. Bantustans acted as little more then holding areas for cheap migrant labor for white businesses. Despite this the Apartheid government tried desperately to legitimize their project by claiming that these areas could and would become independent African owned states (that would be completely dependent and subservient to South Africa of course, as was the case of Transkei). One of the largest Bantustans was KwaZulu which was predominately made up of ethnic Zulus and one of the most important areas the Apartheid state was attempting to solidify in their Grand Apartheid scheme.

Lets rewind a bit now to 1979-1980. Up to this point ethnic Zulus have been participating in large numbers in the African National Congress (ANC), however the ANC has been forced into exile since being banned in 1960. As such many Zulus have been rallying around Inkatha which was formed by Mangosuthu Buthelezi in 1975 and called itself and cultural liberation movement for Zulus. Buthelezi and Inkatha incorporated the Zulu Royal Family and myths and history of Shaka Zulu heavily into their personal cultural pride.

Initially, Buthelezi and Inkatha worked hand in hand with the ANC. But that all changed at 1979 meeting in London about the future of the ANC. Leadership in the ANC-in-exile wanted to mobilize Inkatha further to help their cause and this included the violent struggle. Buthelezi was greatly opposed to the use of violence and he had no interesting in ceding any control over his movement. Ironically, this would turn the "non-violent" Inkatha and ANC into war with each other. Violence inside South Africa became increasingly black on black, Inkatha versus ANC during the mid to late 1980s. A component of this violence was ethnic- the Zulu Inkatha vs the "Xhosa dominated" ANC (it is worth noting that the ANC was not actually Xhosa dominated and many Zulus also continued to participate in the ANC). This schism did push Buthelezi and Inkatha to decide to work closely with Apartheid state against their mutual enemy, the ANC. Many in the Apartheid government came to believe their own and Inkatha's propaganda that all Zulus really did side with Inkatha, and had a more conservative bend to them. As such many Apartheid officials saw Zulus as "the good ones" fighting along side them against the communist ANC menace. Given this relationship perhaps the SABC felt that Shaka Zulu (an important figure in Inkatha propaganda) was a "safe" character to use that bolstered the image of their ally against the ANC. It is worth noting that Shaka Zulu, to many black South Africans is not the universal anti-imperialist African icon often portrayed in the west. We have to remember Shaka Zulu conquered many other ethnic groups and not all remember him so fondly.

Speaking to Shaka Zulu's representation I have found a number of reviews that argue that despite Shaka Zulu being a leading character and cunning ruler, his representation is rife with racist depictions and archetypes. The most blatant is the shows misrepresentation of traditional Zulu religion and customs. The witchdoctor character is constantly pointed out as racist caricature and reducing traditional religion to bland and misplaced "African mysticism." Additionally, the white characters are apparently often shown as smarter, wiser, and more rational than Shaka. I would also argue from what I have read that in the series it seems Shaka Zulu fits well into the "Noble Savage" racist architype. The "Noble Savage" comes to instantly know English, agree with western (particularly Christian) morals and values, but retains enough "indigenous qualities" to remain foreign and distinctly not white. So it would seem the SABC did not stray to far from Apartheid racial attitude norms with Shaka Zulu. In my opinion, I would not be surprised if the SABC was attempting to shoot the gap of creating a show that engaged blacks (particularly Zulus) with an engaging black leader while also remaining in the confides of racial attitudes and politically acceptable understanding of ethnic Zulus in 1980s Apartheid South Africa that Whites would expect.

I can provide a whole host of sources for Inkatha and their relationship with Apartheid state but for starters I would recommend Appetite for Power: Buthelezi's Inkatha and South Africa by Gerhard Mare and Georgina Hamilton

For more reading on the "Noble Savage" I would have to go with: The Myth of the Noble Savage by Ter Ellingson although from what I remember he focuses more on the North American context

I hope this helps :)