access non-standard skills (classes)

I understand the motives for making all skills available to all players. In that regard, I purpose that anything related to 'other skills' in the skill tree be extremely difficult and resource intensive to work with in the game. Meaning it is difficult to do what the designers initially would rather have made not at all possible at all.

First off, (nearly) permanently purging a skill:
Players must purge existing skills to access hidden or advance skills
Players must reduce a skill on the tree to it's minimum level points and minimum development points amount (the green bar) before beginning a purge.
A skill cannot be purged until all skills under it in the tree have been purged. For example, a player cannot begin to purge Gust until Discharge, Air's Embrace, Dash, and Rapid Discharge have all been purged. Likewise Air's Embrace cannot be purged until Shield of Air has been purged. And so on.
Once a skill is zeroed, a player must find and talk to a specific NPC to purge a specific skill. ie: Jerry in Owl's head knows how to purge Summon Air Elemental. The specific NPC is unique to the player. Meaning a player can tell another play where to go to begin a purge. Players must discover their purge beginning NPCs all on their own. ie: Jerry in Owl's head knows how to purge Summon Air Elemental but only for zerothis arathorn.
The NPC will have a series of tasks "Necessary to gain the ability to purge SKILLX". They will be also informed "do not speak of this purge or this task to anyone else, especially outlanders. Do not speak to me again until you have completely done as I have stated. If you fall short in any aspect of this task you will need to begin the quest again. For example, slay 100 bears and bring me 3 pristine bear heads (note, the bear heads can be purchased but the slayings cannot be bought). When the player returns to the NPC with the heads and having slain 100 or more bears, they NPC will give them the next necessary task. Each task is two-fold, accomplished with action and acquisition. Any actions will do, talking, slaying, crafting, giving, stealing, traveling, etc. Items can also be something unique and untradable for the more difficult tasks. Quests for skills farther up the tree are easier than ones closer to the root. Purging a root skill should be insanely hard (unless the tree has just one skill, then merely almost insane).
If the player uses the skill they are trying to purge, then they will be prominently informed of the infraction and must begin the entire ordeal again. If the player returns short of the task (ie: 99 slayings or 2 heads from the above example), then they will be prominently informed of the infraction must begin the entire ordeal again. All in game chat is monitored to catch the player talking about the purge or task ("bear", "head", "purge", and variants of these words for the above example). If the player speaks of the purge or task then they will be prominently informed of the infraction must begin the entire ordeal again. When the player is on a purge quest, they will encounter situations specifically to temp them into failing the quest by saying a forbidden word or using the forbid skill. For starters, immediately after beginning a purge quest, the NPC will ask a question and a forbidden word will appear as a possible answer (let the player make this mistake now, not 120 hours into the quest later). Reading this, you may notice that working one's way down the skill tree to the root is exponentially difficult. Players are advised to not train in any skill they may want to purge later. Once the purge quest is complete. The skill is marked purged in the Skills window and that character will have to perform multiple Epic Greek Mythian trials to get it back.

So, that is my skill purging proposal. Time to talk about bonus/hidden skills.

Advancement beyond Grand Master (Epic Grand Master?):
Gaining these would be like purging, only harder.
Perhaps in only one adventuring skill and one crafting skill. Players could gain access to bonus beyond grand master. If limited to one of these, it would require purging 10 root skills.

Hidden Skills:
Gaining these would be like purging, only harder.Sky's the limit for what these would be. But I will purpose some specific ideas.
Weapon specialty skill. Such as, Dagger, Short Bow, Long Bow, Crossbow, Short Sword, Long Sword, Two-handed Sword, Axe, Two-handed Axe, Staff, Mace, War Hammer, Spear, Halberd, etc...
Specific Weapon bound Skill. A branch of the above which applies to one and only weapon that the player chooses (ie: Possessed Black Sword. but this would not limit the player to only one weapon.
Craft specialty skill. Such as instruments, bows, swords, armor, containers, clothing, etc...
Specific craft specialty skill subset of Craft specialty. Such as Pianos, Plate Armor, Cabinets, etc...
Epic Leap skill
Tree Climbing
Martial arts
Looting