I'd imagine it will be rated M myself, while we haven't seen any gore and as far as we know there probably isn't any nudity, swearing or explicit six, the fact is that the M rating can cover a pretty broad range of content, most likely because it's the highest rating a game can get short of AO, which is pretty much a death sentence as far as sales are concerned and is really only reserved for games that are literally interactive pormography and other such extreme things, I mean, the fact that both Oblivion and Fallout 3 have the same rating is the perfect evidence. Granted, Oblivion was rated T upon release, but it's rating is now M, so obviously ESRB felt that it deserved that rating, even though it's pretty tame as far as M rated games go. There isn't really all that much blood and it dissappears pretty quickly, and the only gore is in the environment and zombie models, and it's really not all that detailed, and what language it has is pretty mild, really no worse than what you might hear on American TV, and the only sixual content in the game is implied. Fallout 3 on the other hand has some fairly extreme gore, you get dismemberments and exploding limbs and no shortage of blood, and a lot of the ambient gore in the game is also pretty graphic, just look at all the multilated corpses the raiders like to hang around their hideouts or the bags full of multilated body parts super mutants like to collect for some reason. Not to mention there's no shortage of swearing, though in terms of sixual content, I'd say New Vegas is more extreme even though nothing is actually shown, I mean, you can even spend "quality time" with a robot, that's something you don't see in many games, but it's still rated M. Regardless, though, if ESRB thought Oblivion deserved to be rerated to M, I'll be quite surprised if Skyrim gets a T rating.
I don't like how the 'M' option is glorified as if that makes it a better game, but it will be M. Others already covered the rating thing.
I wouldn't necessarily say an M rating makes a better game. Some games don't have lots of blood and gore because they don't need it, and adding them in won't necessarily help the game at all. But if you're afraid of getting an M rating, then there's little chance that you'll be able to make the best game possible, as if you aim for a lower rating, you may be inclined to leave more extreme content out even when it would benefit the game. To truly produce the best game possible you should develop it without a specific rating in mind, and do whatever will make the best game possible, otherwise, whether you add things purely for the sake of increasing the rating or cut some things to keep it down, it may be detrimental to the finished product. Still, an M rating does not automatically make a good game, any more than a T or lower rating automatically makes a bad one.