I cannot really speak much about vocal. I'm really at a loss about what could be behind the doors, perhaps someone associated with Zaros? I just hope it's an interesting person and that there's a reason to it. Kill, fight, and stab." Update
I am praying that the boss uses the random Dungeon Generator. AS for collaboration, why not use an element where the player is disabled one player while another needs to remove them, it's the simplest way. In reality, if they use a random dungeon generator it would need to have a maximum level for each of the challenges, so that you won't have to deal with problems in dung, when half of the dungeon gets cut off due to a single door.
I think that the idea of disabling is a great idea and would tie in well with the idea that we need collaboration. It could be possible to take To'kash's deep freeze attack and focus on one person only. It could also last for an extended time period before it would melt (not infinite, though so even if you're trapped by yourself, there's a chance to escape). This would make it more difficult for players to work together.
I envision tougher bosses getting many Dung-style bosses, with nothing that you can do to win. Although some bosses are less effective than others (Lexicus is one example) I think that varying the methods required to take down bosses can make for more exciting boss battles.
Jagex and the dangers of A Half-Assed Wildy
With all the excitement about revival of wilderness in the game, I'll examine what this would mean to the game. How the new mechanics of the last few years would interact with "the wild" and the potential problems this could create.