Sure, the lead game developer said that they have better compression methods now, and with the new XBOX disc format that could add 1GB of extra space, this could be a none issue.
But I would hope that they don't cut content just to try to squeez it into one disc. I also know that an open world RPG would be nightmarish to play by switching between 2 disks, Skyrim WILL be 1 disk, and Microsoft does not support the requirement to preload content via extra discs.
So I would suggest to Bethesda to throw all the content they can into Skyrim to blow anything else out of the water. If they happen to go over that ~9GB range, then save the extra content as extra dungeons that can be downloaded as free DLC's when the game is released. This way, ppl don't have to download them if they don't want and the few extra dungeons won't be missed since the Radiant AI will choose different locations for quests. But if we want the full content that a PC would enjoy, we could download the extra dungeons.
Would anyone mind downloading free DLCs at launch for hypothetical full content?