But don't you do that already? Really - how many players race through the main quest first and then do everything else? A consistent aspect of player feedback is that people have a strong tendency to get sidetracked. In theory, the game already tells you the end of the world is upon us and you'd better do something about it - people nevertheless have no problem justfying to themeslves fetching Amrin's sword from some bandits is worth their time. Particularly if they want some free training. As it is, the game requires suspension of disbelief that virtually all the quests are meaningless crap compared to stopping THE END OF THE WORLD. Why would you even bother with the thieves guild faced with something so apocalyptic? Or bother with killing random nobodies for the dark brotherhood? the game structure would be fundamentally identical. The only drawback to, say, not finishing the thieves guild questline is if the end told you what your actions with the thieves guild led to in the long term.
That's true, there is the question of how much sense it makes to get sidetracked in the first place. The right amount of urgency in the main quest is another issue that often gets talked about. Some of the earlier games were less "OMG the world's going to end!". Daggerfall was mostly about investigating something that happened in the past and you were mostly in the dark about what was going on, Arena had the villain win before the game started, and in Morrowind the main quest NPCs encourage you to join guilds and do other things to build your skills to improve your chances.
I don't like to rush through the main quest, or ignore it for long periods of time, but if they send me across Skyrim for something I'll take a few stops along the way. If you're expecting to be facing a dragon god someday, getting as much of an edge as you can with free training and the resources of a guild could be justifiable as worth spending time on.
I like the books idea - the problem is they'd be basicaly telling the future - one you're free to go and contradict by, say, killing somebody. But maybe if it constituted a prophecy that's more likely to happen because of what you did, that could be really interesting. Actually, you could even unlock, say, some sort of ending that tells you what you did is going to cause, but you can play on anyway - as long as you're aware you may contradict it by your subsequent actions and the existing gameworld may not make much sense in klight of your actions - which let's face it, it doesn't now. It doesn't have to stop post MQ play - as long as you don't care about post MQ play being more nonsensical than it is already.
Yeah, it'd have to be shown as a possibility rather than something set in stone in case of that. I was trying to come up with a compromise that'd let people keep playing, but also be able to show repurcussions of doing certain things. It's kind of an "out there" idea, so it'd probably be like the Warp in the West: could be cool for one game, but maybe not something that'd make a permanent solution.