I know it's very quite early to speculate about this but...
How do you think high end raiding guilds will decide to level up in the expansion in order to reach the maximum proficiency? Every member will do it at its own pace? or instead of 40man raids there will be eight 5man groups to clear instances all day all nights? or maybe even organized grind groups?

on a side note, will we get to see raid instances of new and different dimensions? say like 15man, 30man, 60man?

We are going to have no raids or anything for 3 months because Gurg is going to do every single quest in the expansion and leave himself logged on outside inns so he doesn't get any rest XP and level up too fast. I wish I was joking.

Is VC easier at level 20, or level 30? There's not really an incentive to stop until you cap out, as even if there was loot that you desired from the lvl 60-70 instances, you could clear them much faster, and easier once you were level capped.

I'll personally try to see as much of the 61-69 content as I can along the way. I'm not going to stop and farm it, but I play the game for fun, not as a race. I don't play alts, so if I powergrind to 70 I'm just cheating myself out of a shitload of content along the way, as I see it. I'll do as many quests as I can while leveling, and check out all the 5-mans at an appropriate level.

As for our formal raid plans, it'll be no different than it was 1.5 years ago. I'm sure we'll have a first wave of people on vacation and the like with tons of time to play, and they'll start doing 10-man raids like Karazhan at 70 while the rest of us catch up. Once we have 40 people at 70, we'll start the 40-man content. No real mystery to it. One advantage for us is that as a large guild, I'm sure we'll have enough level 70s within a decent timeframe, without having to put lots of pressure on every individual to keep leveling because they're needed for guild raids. I can see that being a major issue in smaller guilds with an active roster of 50-60 players.

I suppose that depends on what your goal with playing the game is.
If you wait doing all the 61-70 content until its trivial for you some of the point is lost. (On the other hand much of the content will be trivial anyway because content has to be designed for casual players and not for people in T3)

I'll probably do something similar with guildies. Try and quest as much of the new content and instances together. Honestly, to me, that was the best part of WoW, not grinding end-game instances over and over... the discovery phase is so much more fun.