In the main story line, when you defeat the Empire as the Stormcloaks:
Ulfric rescinds his earlier statement, saying he supports the decision of the Moot, whether he is crowned King or not.
Which means Ulfric may or may not be crowned High King of Skyrim. I can't seem to find any information about Elisif becoming High Queen.
In the end, who becomes the true ruler of Skyrim? The player can choose for themselves who may become the king or queen, but is there any hard-wired true ending in the lore of The Elder Scrolls?