From information revealed during the QuakeCon demos, we have some new details about a faction known as The Stormcloaks, which would perhaps seem to be the Rebel forces shown http://www.scharesoft.de/joomla/almanach/images/1/1f/Artwork_-_Art_of_Skyrim_-_Himmelsrand-Karte.jpg, which clearly shows REBELS based at Windhelm and EMPIRE based at Solitude.
From Andrew Reiner's Walkthrough:
an encounter with Stormcloaks on the banks of a river, north of Riverwood, in White Hold
"Continuing down the path on the other side of the river, I stumbled across a group of Stormcloak soldiers escorting a prisoner. When I approached the group a hostile soldier blurted out, "Citizen, I'm warning you." Then I was presented three of choices. I could do nothing, free the prisoner, or free the prisoner and give him an item, which I assumed in this case would be a weapon so he could defend himself against his captors. Considering that there were three guards with their swords drawn and I was a mere level one character, I opted to stay out of it. As soon as I moved away, the soldiers returned their weapons to their sheathes."
Source: http://www.gameinformer.com/games/the_elder_scrolls_v_skyrim/b/xbox360/archive/2011/08/05/skyrim-hands-on-impressions.aspx
The dialogue "Citizen, I'm warning you," suggests this faction is quite powerful, at least in the region of White Hold where the encounter took place. They seem to be an established military authority, rather than a group of rebel agitators lurking in the shadows.
Who do you think the prisoner is? An important member of the Loyalist Empire faction? If you help him escape, do you think that would that make it impossible for you to join the Stormcloaks later?
Also, if you look at the map, there is river that winds its way north of Riverwood, meandering to the Northeast, eventually pouring out into the sea North of Windhelm. Do you think the Stormcloaks control White Hold as well as Eastmarch (the Hold containing Windhelm)? Link to fan-created political map: http://img168.imageshack.us/img168/1641/skmapxyzpoliticalif7.jpg
Since the Companions are based in Whiterun, they must certainly come in contact with the Stormcloaks from time to time. Do you think they will be in conflict with them, supportive or neutral?
Also the description of this encounter suggests more nuance and shades of grey in terms of whether the Stormcloaks or the Empire are "good" or "bad". Granted, this is a small encounter and we know little about the motivations for these factions, but do you think this offers hope for some sort of moral ambiguity?
From Kevin Kelly's G4TV Walkthrough:
Rumors of the Stormcloak rebellion whispered by townspeople in Riverwood:
"Nearby was the town of Riverwood, where some inhabitants began telling me about the Stormcloak rebellion, and I was given a task to find and join that rebellion."
Source: http://www.g4tv.com/games/xbox-360/64714/the-elder-scrolls-5-skyrim/articles/75197/the-elder-scrolls-5-skyrim-hands-on-preview-time-flies-when-youre-dual-wielding-fire-spells/#ixzz1UD8fGnef
This would certainly seem to suggest it is possible for the PC to join the Stormcloaks - one more joinable faction confirmed. Unless the author misunderstood some of the NPC dialogue.