I would really like this for all guilds. Like in oblivion, all i wanted to do was play as the blackwood company, not the fighters guild
Me too, I have always wanted this.
Yeah, it would have been nice in OB to play as the necromancers or the blackwood company but remember while BGS wants you to be able to "go anywhere do anything" they want it done in a way that leads to something they can control for the next game. If the necromancers won in OB then even though it's 200 years later and there isn't a Mage Guild they would have to customize it to your game and they want the hero of the last game to just be a generic hero so you can start fresh in each instance. Does that make sense?
That is a good point, but it can be controlled. I'll use the Mage Guild vs the Necromancers as an example. The endgame of the Mage Guild in Oblivion was basically MG vs Mannimarco correct? Well imagine a world where after doing so of the recommendation quests you start the Cheydinhal one (first instance of Necromancy, with Falcar). Instead of him vanishing after trying to drown him, you and Deetsan track him down and confront him. In the dialog before the battle, Falcar attempts to convince you to join the Necromancers if you want to be truly powerful. You can then kill Deetsan and join him. This unlocks an alternate questline, which pits you against the Mage Guild, but can have either the same ending, or a tweaked one. For example the Mage Guild wouldn't fall because Traven and his champion (would be you if you were in the MG) failed to defeat Mannimarco. Maybe the champion does a lot of damage to him, but Mannimarco flees before perishing. You are then left without a leader in those parts, so you take over for the King of Worms. It is basically the same thing, choosing the other side just can't result in any HUGE changes at the end.
Besides, the only thing that the main person (Nerevarine, Champion of Cyrodiil, Dragonborn) does is the Main quest, we never got confirmation about any guild quests from Morrowind in Oblivion. That was like 6 years, this time it is 200. The only thing that really needs to remain the same no matter what is the Main Quest.