No, you're not going to be able to skin other players. If you can't milk or tan the hide of a tauren, then you're not going to be able to take the skin off a worgen either. Of course this is no official answer to this, but I'd be willing to be all the gold I've got that I'm right.
"Regarding the recent changes in AoE cap, then my question is: why does AOE have to be capped at all? What's the rationale behind it?"
Prior to BC you had no cap on AoE damage. This lead to rather silly things like mages and warlocks taking down entire zones with their AoE spells. I even did a few instances with a very well geared prot pally (a rarity in those days) who would gather up a hundred mobs and the two T3 mages would blast everything down before the priest went out of mana. Not exactly the way the game should be played, so Blizzard implemented the AoE cap in BC. They're just refining it now.
"Why can't tabards be turned off like helms and cloaks?"
No official answer on this, but think of necessity. You can't go without a cloak or helm (assuming you don't want to fail at WoW). You can go without a tabard. Also, back in the day cloaks and helms were pretty fugly. Today they're not as bad, but a lot of players are used to seeing their heads and tails no matter what equipment they have on. I wouldn't put it past Blizzard to allow some gear to be visibly "turned off", however. It's a feature other games have, and those usually make their way into WoW eventually.
"The first fight has two giant Jormungar Worms that tunnel underground and pop back up elsewhere throughout the fight against them. However, before the fifth fight begins, we learn that the ground is hollow and that it can break fairly easily. Where do these worms burrow? Wouldn't they just fall down as soon as they go underground?"
Look for wormsign, you'll be able to tell where they hide. May your knife chip and shatter.
"One of my professions is Inscription and I used to make gold out of selling the decks that can be handed in for trinkets at darkmoon faire. However, since the introduction of more gear in ToC and now Onyxia the value of the decks has fallen through the floor. Is there any chance Blizzard will give these decks/trinkets some sort of boost or is inscription now a complete waste of a time?"
Highly unlikely. The devaluing of crafted equipment is just part of the progression of the game. It's unfortunate that such expensive items like the Darkmoon cards are devalued so much, but it happens; and usually right around the time of the third tier of raiding. Remember back to BC, once you got into Mount Hyjal and the Black Temple the level 70 Darkmoon cards were replaced relatively quickly.
With the exception of the damned Dragonspine Trophy. That thing never dropped and would never be replaced by any piece of gear. Period.
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