Just as the title says. A system similar to a rythm game that uses the existing keyboard display UI to teach players ability rotations. It doesn't have to be anything fancy. Just a simple system that allows players to choose skills from their character and input it into a chain, and then once they begin it shows each ability in order by displaying the key combo for it and then displays the next ability in the chain once the previous ability has been successfully activated. 

I believe this is something that could benefit players of all skill levels when they're trying to learn new classes. It can get overwhelming and pretty confusing quickly when a class might have 3-4 recommended ability combos and all of them include like 10+ abilities. Sure, it's not a necessary feature, but I believe it's a good QOL improvement. 

You could then add simple additions like the ability to save ability chains so that you can come back and practice any time you want without having to redo everything. Or later down the line a more complicated addition would be a feature that allows players to easily share custom chains with each other. Eve Online had a similar feature where players could share ship builds by the game extracting the build as a text note directly to their clipboard which another player could then copy and have the game read the build from the copied text. 

About the only thing that I could see being overly complicated/wonky about the whole idea is finding a polished way to deal with timed skills that can only be used in a small window following another skill. 

The problem is, I don't think PA Devs actually know their own Key Combos.  A lot of the skill interactions are not listed anywhere and get discovered on accident.  This means players have to teach each other, Because BDO didn't intend these interactions initially.

This.

Wut? Literally doesn't make sense. If 1 skill has a unique interaction with another one then it had to have to been specifically made as such. Something like that doesn't magically appear on it's own unless you're referring to a bugged mechanic. But yes you're right in saying that tooltips are poorly made. I know of a few different skills where all it says is "Can be used with other skills". 

And PA can't magically forget about these special interactions as it's highly likely that they have a database that keeps track of this stuff for them. 

That kinda is the point, the animation cancels, initially were a bug, and PA just decided to not overwright the animation cancels.  The game is not designed to do those cancels.

Lets take an unintended interaction.  Lets take Chase for example, it moves at a set speed, W+RMB or WW moves decently fast on it's own.  However if you bind WW to a key via the in game Action Keys and hold LMB you almost triple your speed.  No where does it say that you can increase your speed by almost 3 fold doing that.  This is actually a bugged interaction that has been in the game since day 1 of Musa/Maehwa.  

I wasn't even talking about interactions like that. When I say special interactions I'm talking about things like using BTB and then Spinner does a special attack that counts as spinners 3rd hit to proc the attack speed buff. What you're referring to is a straight up bug, and this system if it were to exist doesn't have to be able to teach people things like that. 

There is a skill trainer that can help you learn a class.

They're called people who main the class and know what theyr'e doing.

Find them.

Oh wow, we got a badass over here. Well Mr. badass I'm sure as a resident genius it's more than ezpz enough for you to look at a skill guide and immediately pick up whatever combination of abilities it tells you to use without a single hitch. However not everyone can be as godly of an individual as yourself. So some people, not the badass super 1000 IQ mega minds like yourself, but some, might actually enjoy a little UI menu that shows them what keys to press so they can learn skill chains quicker. But of course the struggles of peasants such as ourselves must be incomprehensible to an ascended being like yourself so I earnestly apologize for trying to explain such a concept to you. Have a wonderful day!

Skill guide?  When did I say "look up a skill guide"?  I said find someone, AKA a person, AKA a human, AKA someone who plays the class you're trying to learn, and go learn from them 1 on 1.  I learned a lot about Sorc from people who main the class by meeting them in-game, also by getting my butt handed to me on many occasion.  The game has no clear-cut, A B C D handbook in-game on how to operate a class, which is what you're asking for.

We play an MMORPG.  So how's it not make sense to talk to people in-game or other means?  There are class specific Discords, for example.  Would it be cool if the game held your hand and told you everything about combat?  Like, "Press this, press that and that for combo A, and do this for combo B"?  Not even sure how to answer that except with an example from another game with great PvP - Street Fighter.

Look at fighting games like Street Fighter.  Even Tekken.  All they do is give you the basic commands for moves in the Command List -- and players spend hundreds, even thousands, of hours in Training Mode to figure out the best ways to link moves, what moves are plus or minus on block or not, analyze frame data, and find out all the combos available to master a charcater.  Same concept in BDO.  Yes, those are purely fighting games and BDO is much more, but at a base level when it comes to COMBAT, same concept of "figure it out yourself" remains.

For me, that's where the FUN comes from.  It's a challenge to learn a new class / SF character.  And overcoming that challenge and knowing that YOU found out how, makes for satisfaction and a REWARD for your EFFORT. 

You're literally asking for the reward (knowing how to pilot a class well) with less effort (playing the class, trail and error, discovery, etc.) at the end of the day.  Which is your opinion / request, cool.  I just don't agree.

Actually they are both the exact same thing.  What I mentioned is just a more simple version of an unintended interaction.

Also, you have Players who can teach you better than any Dev can, use the community resources like Youtube and search your class or look on Twitch for said class like was suggested here.

Your response of

was uncalled for.  Someone tried to help you, and you just spat in their face.  I tried to explain why what you were asking for wasn't possible and you just wanted to argue.  I highly doubt you could learn from an in game tutorial on all the combos with your "I know better and I'm not going to listen" attitude.