After the referendum vote in January 2011 that gave South Sudan its independence, International Crisis Group’s Zack Vertin pointed to some of the challenges that lay ahead for the new country. One of the most important was the issue of internal political pluralism:
The rebel movement turned governing party — the Sudan People’s Liberation Movement — dominates the political arena. Since the end of the war, opposition voices have suppressed grievances and taken a back seat to the SPLM so as to preserve the goal shared by all southerners — self-determination. But now that the vote has been cast, that common denominator is gone. When the jubilation of last week’s vote subsides, the political environment will slowly begin to transform. The current leadership must respond accordingly, recognizing that a genuine opening of political space is both necessary and in their long-term interest. They must find a way to equitably manage the South’s own diversity, lest they simply duplicate the sort of autocratic regime they’ve finally managed to escape.
Nine months later, the issue remains. Over the weekend, the South Sudanese opposition spoke out, alleging that the ruling party was harassing its members:
A major South Sudanese opposition party, the Sudan People’s Liberation Movement for Democratic Change (SPLM-DC) on Sunday protested against the “targeted” arrest of its members.
Onyoti Adigo, who leads the largest opposition party in the National Legislative Assembly, told Sudan Tribune on Sunday said that three diplomats aligned to his party were picked up at gunpoint on Friday while leaving the ministry of foreign affairs and international cooperation.
He named James Okuk as one of the members being held in undisclosed location by South Sudan’s security services for allegedly for writing against president on the internet. Some other SPLM-DC members including Sabino Tom who were arrested with James have been freed.
As the head of the United Nations Mission in South Sudan said in September, the world will be watching to see how the new country performs on pluralism and other issues. I doubt that autocratic behavior by the ruling party would jeopardize funding from donors immediately, but in the long run outside observers may grow increasingly frustrated if the ruling party proves unwilling to open the political space to a greater degree. Internally, moreover, unmet political demands may give rise to violence; the country is already dealing with several rebel movements.
The region surrounding South Sudan is flush with former rebels, revolutionaries, and military leaders who are still in power – President Idriss Deby of Chad, President Omar al Bashir of (North) Sudan, President Robert Mugabe of Zimbabwe, and President Yoweri Museveni of Uganda, to name a few – but there is a lot of pressure on the SPLM in South Sudan to take a different path.
Sahel Blog 
Perhaps one difference between South Sudan and other post-revolutionary governments in places like Zimbabwe, Uganda and Eritrea (and, increasingly, Rwanda) is that the charismatic figurehead of the revolution is not here to govern in the post-war phase. Such leaders are notoriously difficult to flush from power, as you suggest. It is possible that the SPLM may follow a different path without Mr Garang to lead them.
Kiir presents as a reasonable man, however perhaps an even bigger challenge awaits South Sudan – the creation of a truly plural political landscape. The SPLM, like the ANC in South Africa, is credited with winning freedom for the people. This may give them untrammelled power through genuinely free and fair elections for many years to come, during which time the party is likely to become less and less committed to the idea that they must one day hand over power.
I have doubts as to whether they’re even considering fair and free elections.