I don't think anyone will disagree with this one.

That (another guild suddenly asking for the same item you are fetching for a quest, as mentioned in the original post) just sounds so cool. I would love that. It's a way to make the guilds seem more aware of each others' existence. Oblivion seemed very disjointed as there was no interaction between guilds. Having to consider where your loyalties lie is an interesting choice to make. Stuff like this breathes life into a game.

I think more quests should be failable, maybe due to time dependence as mentioned above. Let's say you get far along a certain guild's questline, but have messed up a lot of quests along the way. You should be given some drudge work, have to bribe / charm / asassinate your way to the top, or in extreme cases just don't get to advance any further along this questline. In which case it would be nice if most guilds had a 'rival' like they did to some extent in Morrowind. You could come back later and punish the guild master who kicked sand in your face.

all great ideas...but on the subject of guilds opposing each other...it sounds good but only if they can doit in a way that, doesnt break the quest lines. i remember every time i played MW i would get stuck on one quest for...either the fighter or mages guild and not be able to advance any further because i couldnt get the object needed from a member of the thieves guild, without stealing or killing a fellow member and getting booted. even with my people skills beefed up she would never give me the item i needed. i eventually figured out a way to advance them all. but i had to look it up.

ps...sorry im to lazy to caps my sentences.