Flame Orb is not channeled. It may have a cast time, but after that is fire and forget. We want to try the line idea because there aren't any spells that work that way currently. Giving it a target to follow makes it feel more like a fancy dot – useful perhaps, but nothing that feels really new. It will be balanced for single-target damage, but if you can launch it in such a way that it will hit multiple targets, then you're just being awesome.
Wall of Fog is not channeled. We don't know yet how wide it will be, but wide enough so that it feels more like a trip-wire than an area like Frost Trap.
We like the basic gameplay of Hot Streak. With lower crit rates all around, we hope that it will feel more like a bonus when it's up rather than a penalty when it refuses to stay up. We may lower the magnitude overall for the same reason.
On Arcane Missiles, the basic spell is pretty cool. The problem is the way the spell works makes the current design hard to balance. It's either too expensive and low damage or the opposite problem. This is particularly true at low level, and meanwhile we think the mage experience at low level is also a little too repetitive. The change is that you can't hit Arcane Missiles whenever you want. The icon is just grayed out. However, when you deal damage, you have a chance to get Arcane Missiles to light up and then you definitely want to hit it. At higher levels Fire and Frost may eventually phase it out in preference for other spells, or if we like the mechanic, it may be something even Fire and Frost do, just less often than Arcane.
On the topic of mastery bonuses, understand that this is a new design for us and very few people have seen them in action yet. We run the risk of specific masteries being so generic that the mastery stat isn't interesting or so complex that what players really like about playing a certain spec gets turned on its head. This is the kind of thing that will require a lot of iteration and the reason we're trying to cover the whole gamut of relatively complex to relatively simple to see what feels right.
The reason behind Deathfrost (Frost mastery) isn't to get Frost to spam Frostbolt more. It's to get mages to spam Frostbolt less. If you hit nothing but Frostbolt, you're wasting the Deathfrost bonus.
We're shifting food and water to higher level because we don't want players to have so much down time at lower level. We're not trying to make it harder to level; we're reducing the need to drink or eat so we're bumping the actual food and water (though it's really foodwater in the case of mages) higher.
The intent behind Mana Adapt (Arcane mastery) is that Arcane currently has a pretty fun mana management game going, at least at relatively high level. We thought it would be fun to extend that concept even further to where Arcane mages that use the mechanics to keep their mana high would do higher dps. I find many of the predictions that Arcane is doomed in PvE based on the very limited information you have at the moment to be quite premature.
On Time Warp vs. Bloodlust, we are really trying to give groups flexibility in who they bring to 10 player raids to an even greater extent than we did in Lich King. We heard over and over that shaman still felt like the one mandatory class in any raid. The more we hear "now there will be no reason to take me over X class / spec" the happier we will be. The reason should be that you're a good player, not that your mere presence makes everyone else perform better. It's fun to feel more powerful in a group – we get that, and we aren't going to completely marginalize group synergy. But it needs to come secondary to the skill of the players involved.
I understand some mages really like Fire Ward or Dampen Magic. Perhaps "no clear role" wasn't the best choice of words, but we are trying to remove mechanics from the game that we think aren't really cutting it. When asking players to put more buttons on their action bars from these new spells, we only think it's fair to try and get some bar space back from the least interesting spells. Don't worry so much about balance at this stage. Many things will need to be tweaked. Worry more about whether it ever felt like a fun decision to use these spells.
For everyone focusing on the RMP Arena comp, I really think you're going to see a shift to more PvP concerns in Cataclysm being about Battleground balance. There will still be players playing Arenas for sure, but a lot of the players currently doing Arenas are going to shift to rated BGs instead.