Obviously Celerity has put a lot of thought into this... I remember when Viri first introduced the selectable skills into the classes... It was like WOW, now I have to play three berserkers to figure out what they do and what style I like... And then it was crap! three warriors and three ninjas and three thieves and three rangers... Damn, how much time does he think I have to waste on this game??? And then along come Crusaders with their truly diverse skill sets and I honestly haven't even messed with Psi's... All of a sudden the same old same old became much more diverse and feature rich and intriguing to play and find out what did what...
This is one of those things that can bring that type of replayability out in spades... Almost to the point of being too much, but I think something along the lines of what Celerity is proposing might be good... Especially for a class that seems to be lacking in luster... Although I do happen to remember a few serks that kicked major butt, but they were played by the same people who always kicked major butt... 
I think you do need to be careful about implementing cross class skills at the advanced level... If you give them the cherrys of the warrior class as advanced skills, who is going to be playing warriors??? And yes, this could be implemented with them as well, so that probably wouldn't be a huge factor...
I just think we want to keep the classes somewhat distinct so that they don't become too indistinguishable... And having race perks involved with it is cool too...
Nice job... It is obviously better than re-vamping the whole system, but as it is, it would take a great deal of coding to accomplish... That could be the tricky part...
I think you do need to be careful about implementing cross class skills at the advanced level... If you give them the cherrys of the warrior class as advanced skills, who is going to be playing warriors??? And yes, this could be implemented with them as well, so that probably wouldn't be a huge factor...
Yes, I'm worried about the same. That is why there is a limit on the skill based on the class.
A warrior would be able to choose to upgrade any weapon skills they want to 'master' level, but a zerk or thief might not be able to do that for every weapon.
The hallmark skills of the class can be upgraded. Not all classes can reach 'master' level in all of their skills. A zerk can use a staff, but they can't learn advanced or master staff. An invoker has parry, but they can't upgrade it to advanced or master.
So, warriors are at least as good as other classes with weapons and could be better. A warrior using shield block (master) could be different than a shaman using shield block (basic), if the warrior chose to invest her training into shields. A DK could have a better shield block (advanced) than a shaman (basic), but not as good as the warrior (master). However, a shaman's plague (master) could be upgraded more than a dk's plague (advanced).
I do not think celerity is inferring that a thief could gain the ability to cast sanctuary, or word of recall. (Unless I am reading this wrong.) Basically it allows more customization of each class, and let's the player more directly choose the specialization of those skills/spells. Like say a cleric that is less focused on healing, and more on battle will not have as strong of healing spells, but will be able to dish out some decent damage, and other battle related spells. If I am correct in the way I have interpreted this, I am definitely in for it.
From what I read no class is getting extra skills that other classes have. So that is not changing, don't understand what the fuss was about that. I'm liking this more and more as Cel explains further.
Yes I'm liking this idea more and more. It sounds like it'll be difficult to find two identical combos at 50 at the same time which is a good thing. A character should represent individuality to the player. And lets say you're better at one strategy as a class then another, you can customize him/her to your own strengths. Lets take player A and player B. Player A always fantasized about darknights riding upon horseback utilizing a perflect blend of combat prowess and dark magics, thus proving to be a match for any of the worlds strongest wizards or warriors. While Player B fantasizes about his darknight growing so powerful from the pain and anguish he has consumed from the souls of others that he eventually rises to become the strongest being the lands has everseen. I'm sure I play my dk's differently then the others that were more successful than mines. This could be because they are better at using the strengths inherently designed to be stronger than the tactics I focused on. Lets say we have dk's that focus on spells, melee, charm person. But the current system rewards the player that focuses on melee more. With the way Celerity is describing this, it seems like you can customize your dk to tailor to your own strengths (as a player) without weakening the class (the quick solution we've always resorted to in the past).