Interesting thoughts here, and though I prefer not to speculate too wildly, but.....

Remember that in a largely persistent world and personal storylines, it must be possible to play large parts of the game solo, hence no monk class. This also means reasonable self-heals (already declared), with maybe support for group heals from some racial skills, or class skills. It also should mean that all classes have reasonable damage output.

Now, we already know the following from Arenanet.
"The professions are divided into three categories based on their level of defense — there will be 3 scholars, 3 adventurers and 2 soldiers, which wear light, medium and heavy armor, respectively."
So, we already have one scholar, the Elementalist.
Second scholar? I think there will be at least one full-blown 'summoner' class. GW Necromancer was a novel approach to summoning, and in my humble opinion, the Ritualist was revolutionary. In both cases I can't see Arenanet scrapping soul reaping or sprits. Given the information on skills and weapon set swapping (and therefore its corresponding skillset), it is possible that a hybrid Necro/Rit could work ok, one weapon set allowing minion summons from corpses, and another set to summon spirits. I sometimes run a spirit build on my Rit using Spiteful Spirit as my elite skill (you just know that everything will attack the spirits first :) may as well spread some pain:)).
Third scholar I suspect will be a hexer/debuffer class, probably the Mesmer, again, a class almost unique to GW, and in the hands of a good Mesmer plater, immensely powerful in GW, despite its reputation. Very tricky to play well in PVE parties though so I expect some simplification in Mesmer gameplay.
These 3 scholars would give a balanced choice of gameplay. Note also that Mesmer and Ritualist have both had major reworks recently in GW, and I can't imagine that Arenanet spent so much time and effort doing that if not in anticipation of GW2. The Elementalist's inclusion was a no-brainer.

Soldiers? Well, we have the Warrior already (another no-brainer) As for a Paladin type, we already have that in GW, as the Dervish, poorly implemented for that role I agree, but nevertheless, a Warrior/Monk. Capable melee character with good heals, unfortunately unpleasant to try to do both (it doesn't work on many levels). I suspect here that a Protector/Commander (Paragon) type will be the second soldier, adding to the Warriors shouts for primarily party buffs and maybe condition and hex removal. Somehow I can't imagine that Arenanet made Kormir a God for no reason, and having done so, that they would not utilise her in some way in GW2. This second soldier class is possibly the trickiest to figure out.

Three adventurers pose a problem.
Ranger will be in I think, if for no other reason that it is the most popular character, unfortunately, historically, the most nerfed, and in most of the released artwork there are lots of Rangers :) Giving Warriors a bowskill was a good move as it filled a terrible gap in the Warriors gameplay i.e. sometimes you just need ranged attacks where melee isn't helpful, so I can't see them replacing Rangers. I see them as an interupt/condition spreading pressure class (with pet), and being integral with nature.
Second I would guess a stealth class, Assasin would be favourite, though with a more clearly defined in - damage - out role, rather than the horrible tank role they have developed due to Shadow Form, and poor Assasin players :)
The third adventurer I can't really place to be honest, but if I had to guess, it would be a Sniper of some sort, certainly a 'gun bearer'.

Anyhow, I could go on and on and on and on.... so I will leave my thoughts to wonder again, and think about how many profession names may change, I suspect not many if any, though I do remember reading somewhere that 2 professions will be new :)