Hiya!
So whats your opinion on skills in 5e. Personally I think their half assed. You cant learn new skills but you can pay to learn tool proficiencies, so you can learn to play any instrument but cant learn to sing. Same stat same level all skills are equal, even if the one person/NPC makes a living off being a guide (survival) the cleric with the skill and same stat and level is equal. Just a few of the things I dislike about the 5e skill system. BUT I'm still having loads of fun playing.
I think they needed an option in the DMG for "specializations" or some such; like having "Athletics", and being able to specialize in, say "Climbing"; you would then get, say +2 to Athletics when Climbing, but -1 to Athletics for everything else it's used for. Something like that. Anyway...
Aside from that, I think you are looking at skills (and pretty much the
entirety of the 5e rule set), "backwards". IMHO, you shouldn't be taking the rules and then making the world fit them...you should be taking your world and making the rules fit it.
If you have a "problem", with the rules not allowing, by RAW, a PC to learn an instrument, but not how to sing, then
fix/change it to fit your campaign world. You don't have to wait for some "Canonical True Word From On High" (re: "sage advice", or "tweets", etc), you don't have to wait for some official book to come out with new rules, you don't have to wait for someone else to write something up and put it on the DMGuild for $1. In fact, IMHO, waiting for someone else to do it is going against the spirit of the 5e rules; rulings, not rules. Make it up yourself, based on how and what you want for your campaign.
There is absolutely
nothing stopping you (assuming your DM here) from saying "
Ok, same rules for learning a Tool, but you can learn a specific skill....like "Sing", or "Climb", or "Weaponcrafting". It will fit under whatever skill makes most sense for it. Just run it by me first and we'll work out any details". POOF! Now the 5e rules fit your campaign. Now it's truly
your campaign...not just another cookie-cut world with no unique personal touches. Having a campaign that you and your players can call your own, and actually mean it, is something that
nobody who runs just "another FR campaign using the RAW and official FR stuff" can match. Period. End of discussion.
^_^
Paul L. Ming