1) There is a menace returning to the land. If it is not pure evil, then it's intentions or motives are certainly incompatible with "the good guys." No world peace summits, it's kill or be killed.
2) There is only one hero who could possibly stop said Evil (or simply antagonists)
Now, the first one is...forgivable? At least they didn't use daedra again. But I would have still preferred the civil war in Skyrim to be the main focus. (assuming that's what's meant by "sons of Skyrim spill their own blood." But the inherently evil enemy is dragged on way too much in the fantasy genre. Yes, it's a staple, but so many people do it that it no longer is an homage, but simply cliche. The Orcs of Middle Earth, the Darkspawn of Dragon Age, the Daedra of Oblivion. I want to see more perspective. Was Napolean evil? How about George Washington? Give me some moral ambiguity here.
The second, however, is tenuous. Heroes are real. Throughout history, the outcome of wars, nations, and entire populations of people have depended on the shoulders of one or a small group of men. But, there was no ancient scroll that prophesied Churchill and FDR beating Hitler. It just happened. So, while I admit that the player character will almost always have to be the hero (unless he ignores the main quest) I would prefer he not be "destined." Maybe that's contrary to the Elder Scrolls mythos, where even the future is written down. Certainly, the title "Dragon-Born" implies fate, as he was "born" to fill this role. It would please me greatly though, if there was no prophesy, and your character simply earned that name in one of the early main missions, where after being swallowed by a dragon, he/she cuts himself free, thus becoming "dragon born."