My wife just started playing, and I had no idea skills were locked & hidden now until you do specific things to unlock them. It really confused her.
Is there an addon that adds these locked skills to the skills window, perhaps greyed out and with a tooltip that explains how to unlock each skill? If not, I would like to request one. I posted a comment on harvens improved skills window, but it's been years since I was active, So I don't know if he is active anymore.
Afaik it's not possible to do this without rebuilding the whole game code like it was before they patched it to this disturbung way of skill "exploration"... And I can't think of any dev who would like to invest weeks to build and maintain this, sorry.
I used to write /bug into the chat ingame and told the game devs that this is wrong and annoys the users.
I also asked them to add more explanations and hints, that one realizes how it works (same with "you must wear at least 3 medium/light/heavy armor parts to unlock the armor skills...). It sucks in my opinion and users should be able to change this in the settings between "old way" and "new way".
I'd rather tell you to complain on the official forums as there are already ppl who do, and only the mass will make a change happen (maybe).
I managed to hack GetSkillLineInfo() to have the UI show hidden skills. So far, the best way with the least work is to have it set the advised flag if a hidden skill has unlock instructions. Not all hidden skills do, but this too could be worked on. Unlock instructions seem to always be a string, either empty or containing text.
ifnot avail then advised=advised or unlock~="";end
_1, _2, and _3 are unused. _1 is a number while _2 and _3 are boolean. If I were to guess, I'd say _2 is if the skill can be discovered by the character and _3 is if it has been discovered. That would make _3 a duplicate of avail if so. I'll have to dig around old sources to be sure, if they were ever used at all.
Edit: Digging around, I found this. Guess that answers my question. Though active isn't set on a few hidden skills that should. Ledgermain, Vampire/Werewolf, Guilds, and AvA skills are ones that I found.