i know everybody is gonna be disagreeing on this but im going to throw it out there.
i think it would be insanely cool if you could get rare skills which only 1 person can have of each skill. so if you are lucky you fall over a hidden chest with the given skill and would give you one that cannot be optained by anybody else.
would be cool to fight and then if you are lucky see skills that only 1 person have hence you will almost never see them again.
Or something similar to that, except that the method of getting the skill changes every time someone gets it. Anything ranging from killing a certain number of a monster, to crafting things, to finding it in ruins.
That would be pretty neat.
This actually presents the only way i could see rare/hidden features be presented into the game in a semi-balanced manner 
this got a slighly better response than i exptected. im just waiting now for the people who will yell that its unfair because everybody should be equal xD
I absolutely hate everyone having access to the exact same things. Either very hard to find skills, or such a massive amount of skills is needed for any kind of meaningful diversity in my opinion 
I like the idea, but realizing that new skills cost a lot to develop, maybe a slight adjustment could be proposed that there exists in rare and random places, scrolls teaching rare skills, but one avatar can only accept one of these skills at a time. Furthermore, the skill in the scroll is unknown before use. Once used, the scroll is destroyed. However, a single avatar can use as many of the scrolls found as they want provided they forfeit the previous rare skill.
This should achieve the desired effect.
i am writing a scroll skill system atm. will be up in a few min
If you want to restrict the skill i would rather have that you would need to identify the scroll before being able to use it. Probably through some other kind of skill
This UniquePerson® with a VeryRareReallyUniqueSpecialHiddenSkill® is offline for two month. What are you will to do?
IMHO, this idea is unviable.
Sounds like The teachings from the anime Log Horizon. Still, it sounds like a lot of work to implement though. Since you need to create unique ideas for each skill as well as balancing them at the same time.
The idea is cool, but as far as balancing it so you’re not suddenly the most powerful player, it’s not exactly practical.
This is a great point which I intentionally avoided in my response for fear of people missing the point I was making. I would think that these rare skills are all superficial in nature. Perhaps an increased likelihood of finding treasure or catching an exotic fish or a flamboyantly flashy combat effect that does not have a remarkable damage ability. Most would be happy with an extra light aura added to the avatar or just about anything that is hard to get.
Most everyone wants to feel special about their avatar. Special does not have to mean being the ultimate destroyer of the universe.
One of my favorite effects from WoW was from the food crafted from a lightning fish. It would randomly zap nearby level 1 squirrels and the like wherever I went. However, the side effect was it would also zap nearby passive enemies and get me into trouble too.
Ok, described like this I would totally get behind rare skills. I would not make them unique but rare and hard to obtain. Also, strictly passive and non-combat related. Post 1.0 release.
SAO much lol?
I think this could be neat, but the devs probably dont have the resources to make unique skills and stuff.
Skills could vanish from the game completely due to the finder never returning after getting bored. Secondly I worry about a monopoly on said skills as some people would grind away how much of their free time to acquire said skills. Luck plays a factor but it can also lead to others feeling discouraged due to lack of luck or time.
I agree that I would rather see rare skills that are hard to obtain or obtained through true skill such as a skill at the end of a parkour course or a shooting range. Perhaps even skills to act as achievements such as herb picking bonus’ for having harvested so much farmed food.
But would it really matter that the guy with a slight buff that helps him to do some ridicules small thing disappears from the game?
Again the skill would be part of some loot in a chest and therefore likely be found instead of a weapon/tool or rare material, people wouldn’t get less it would just be some different loot they could find.
Sorta Spoiler to anime SAO Season 1
I totally agree, that reminds me of the anime SAO where Kirito has the unique skill of dual wielding. I would love if by some means players get unique/rare skills. For example, and this is a rough example, if somebody were to stare at the night sky during the night and build there house close to the sky they would learn about the stars. Thus they would obtain the skill of astronomy allowing them to make a telescope which can allow you to see constellations. Such an idea would be amazing. There could be hundreds of skills, like water breathing, flight, or even a skill where you could plant hundreds of trees in an instance thus creating a forest! 
It’s so exciting to think about!
P.S. Thanks for the link to topics about crafting suggestions @Zouls