Serbia: why is Vučić stepping down?

Večer looks at what comes next:

“If Vučić actually resigns, according to the constitution the parliament speaker, Ana Brnabić, would replace him as acting president – but only until presidential elections are held, in which she herself could stand as a candidate. … The rector of the University of Belgrade, Vladan Đokić, has become a symbol of the student resistance movement. Unlike other rectors, he supported the students from the very beginning. … He is seen as a potential rival to Aleksandar Vučić. It is therefore conceivable that he might head a party list in the parliamentary elections, or stand for the presidency himself. A change of government is unlikely to be straightforward, however. Vučić is known as a skilful tactician and a master of political manipulation.”