You say "game changer", but I see it's a game
breaker.
The Elder Scrolls makes "freedom" a key selling point, specifically, we're told it offers freedom to "do whatever you want." While that's not acually strictly accurate as any game is bound to have limitations as to what you can do, and it would probably be more accurate to say "Do whatever you want, within reason." it does promise certain basic aspects of freedom, these include the freedom to ignore the main quest. In fact, I'd say that's the most important part of "freedom" the series promises, as you can't enjoy the freedom to do other things when the main quest is constantly trying to force you into doing it. In past games, I made many characters that never touched the main quest, there was just so many other things to do, and the main quest really wasn't replayable enough to make it worth playing ten or more times. If you punish the player for not doing the main quest within a certain amount of time, than that's no longer an option, you have to get the main quest finished before you can do anything else, or face the concequences, and I'm not going to play through the main quest with every character I make before I can get to the part I actually want to do, I'll stop playing the game entirely, or see if I can find a mod to fix the mistake of giving the main quest a time limit.
Now, it wouldn't be so bad if a few select quests had a time limit where it would be reasonable, like that part in the main quest of Oblivion with the great gate, but those should be limited to special cases that last only for the duration of a specific quest objective, and usually these are situations where something is happening right now which will lead to disasterous concequences if it's not adressed in time, and you can clearly see that said time limit is not far off.
If Bethesda wants people to stay focused on the main quest, than they should make it so interesting that players won't want to be distracted from it, if the only way to get people to focus on your main story is to punish them for failing to do so, than maybe you should ask yourself if it might possibly because your story isn't actually that good.
Its already confirmed in the game. I'll have to find the reference, but in a nutshell, dragons will appear if you havn't faced one in a while. And since dragons are unscripted, they can burn/kill what they please. So you better be the hero at some points or risk being labeled something else by the NPCs.
Just because dragons aren't scripted doesn't mean there aren't limitations on what they can do, it simply means that there isn't a script telling them to specifically to this or that at a specific time. There's still limits to what they can do, it's just that, amongst the behaviors available to them, you can't be sure which one they'll choose at a given time.
And they can't burn or kill anything that's literally impossible for them to destroy or kill, so they'll only be destroying villages if it's actually possible for them to do so, and while it's been stated that there are a few select structures that can be destroyed during the course of the game, I'm guessing that these are limited to things like the saw mills we can destroy or maybe some minor environmental damage like blowing up cars in Fallout 3, which has little lasting concequences. And I have absolutely no doubt that Bethesda has measures in place to prevent dragons from killing major quest givers, whether these characters are actually unkillable, by the player or dragons (I'm thinking mostly main quest characters here, we know side quest characters may be replaced by their reletives if they die, but I highly doubt that Esbern can die and be replaced by his brother or something.) or they automatically take cover in buildings when a dragon starts attacking and don't come back out until the matter is dealt with. This is the company that decided to make even side quest characters unkillable in Oblivion we're talking about here, I think we can safely say they're not going to design the game to allow major quests to be broken by things the player has absolutely no control over and may not always be able to stop.
And we don't know when dragons start appearing, maybe they're like Obliivion gates in that they only show up if you have completed a certain stage of the main quest, which is what I hope, since if I decide to ignore the main quest entirely I don't want to be constantly reminded of the destiny I decided to have nothing to do with on my current character.