Well first of all let me talk about roles in general. Well one of the things that should want to consider when making a class is the shelf life of that class. Or how long can a player play a class before he gets bored of it. Now there different things that come into play like skill shots, number of abilities how difficult it is to master. But lets take a look at the dps role for rangers. But instead of roles lets look at as responsibilities.
If you were to look at the abilities rangers have a dps cc role. So lets say they have those two responsiblities dps and cc chains in pvp and pve. Well I play rangers a lot and want to tell you that those two responsibilities are not enough to keep players playing that class for a long time. They just do not have enough to do to keep the class interesting ounce you hit a hard skill cap. After lest say one year. (although fun factor could change that) I know this sounds odd but lets look at the tank responsibilities
(Want to point out that every class has a dps role even healers when party is full of health so it could be said that rangers only have one additional role cc)
Tank responsibities
Dps still have contribute was much dps as possible but not primary role
Pulling
Holding argo
Target calling which includes putting icons over target heads
CC and interupts
Have to keep track of every ones mana and health in between pulls cannot pull when people are to low on health or mana.
Many times fulling the role of group leader and doing ready checks explaining fights.
So tanks have a full plate when it comes to responsibilities which makes the class ,in my opinion ,makes it more immersive and fun.
Think wandering mist made a post about how healers need more to do or something to that affect. I have never healed before so will not post about that but will say that a healers targeting system and GUI looks more complicated than the average rotation for dps cycle for dps class.
So looks like dps classes has a shortage of responsibilities so think that Archetypes would be a good way to give the player more to do but there are other ways to do that.
Another thing I want to mention is role playing value. For example for Beastmasters if their pet had a danger sense that detected stealthed enemies or undead in the ground like cadaver dogs. Would increase the role playing value of that archetype. Or for rogues if they were able to set trip wires (oddly enough League of Legends Jax already does this) in between dooar posts (concealed) and out in the open (unconcealed). So if a certain Archetype allowed a rogue to do that that would be great. Ninjas and other martial arts class also fall into the rogue category could be the rogue rogue category.
Also want to mention hunter mage like if traps were augmented with with implosion and actually pulled the target into trap increasing radius then imploding making little mushroom at center of trap knocking toon into air only to met by a trap when they land that would be pretty cool. Think this are the types of things players want.
The next topic I want to talk about is a class being able to do everything. Now some people say that makes all the classes the same, but in my opinion it is not what they are doing it is how well they can do it.
Now Ret pallies in WoW have an ability called flash of light. Flash of light is a spammable ability with cast time that serves as a small but decent seflheal or off heal. But the problem with this was that the way the game mechanics was set up that spell could be buffed on a ret pally in such a way that for a short time The Ret pally could fill the role of a healer. (heal someone to full health in 3 or 4 casts.) So if you were in a raid and there was a part of the fight that did damage pally could off heal and really no way that the tank was going to die with additional heals. So it would give raid groups with pally a huge advantage over a group without one so it got
DEMARCATED
Yes gents demarcation is a fancy word for nerf

But Pallies can get an off heal for roleplaying purposes. Decent heal on a long cool like 3 min really does not have to much impact on game just Pally will be able to save people ounce in a while. But if you give pallies an ability on a short cooldown with low mana cost and decent heal then Pally would find himself pushing the heal button a lot more and play more the role of a dps with great heals instead of just a heal.
Now the Protection Pally in Cataclysm also played a dps role. There is a passive ability vengeance that was based on the total damage received while in combat well if you chained pulled the entire dungeound and stayed in combat by the time you got to end of dungeoun you would be doing an insane amount of damage. So that dps role had to demarcated or nerfed.
Now Hunters in WoW have an ability called raor of sacrifice were pets take 20 percent damage of target thing is it was on a 30 second cool down last time I played. Well 20 percent less damage every 30 seconds to help out tank is a huge boost (certain amount of skill required but not too hard) most tank defensive cooldowns were like 2 min and above I think.
But this allowed hunters to play the off tank role on top of their dps cc roles. Also want to add that hunters in WoW had a debuff abilitied called tranquilizing shot. Could be spammed cost 20 energy out of 100 but because it was spammable hunters also had responsibilty to debuff. Worked great in pvp sometimes useful in pve. So just one ability gave him a role mainly because it was spammable and not on a long coold down. Got demarcated (nerfed). Hunters also had a very small 2 percetent heal every 20 second more for role playing purposes which I liked. Yes hunter had a heal that could heal others but so small impact on game extremely small.
So classes can do lots of things and still play their main role. Just should be careful about abilities given.
Another Thing I think you should consider is the needs of the company. When the game rolls out lots of tanks will be need so only makes sense to have more classes fulfill the tank role. So you could have the tank archetype be more impactful than the rest of the archetypes. Really do not think you should tie your self down to all 64 archetypes to a certain level of demarcated roles instead just create them as needed to benefit the game. My personal recommention is to allow warriors warlocks tanking roles. rogue more of a pure dps role over all,hunters off tank role with pet tanking (that means ranger tanks would be allowed to have pets).......point is tank archetypes could have different amount of impact per class.