Is there any basis for a bard class in WoW lore?
The easy answer would be no. Nowhere does it say in WoW that music has any inherent magical power.
But here's the thing. We know that in order to use Arcane magic, it has to be channeled. This can happen either through the spellcaster themselves or through runes, per proxy. Why runes? Runes work, because their shape and patterns mimic the ley lines throughout Azeroth. They channel the energies correspondent to them. (The arcane spellcaster also draws their power from the leylines, to be sure.)
Well, that's nice. So what does this interesting, albeit probably irrelevant WoW lore factoid have to do with the bard class?
Sound creates shapes and patterns, too.
These are called chladni figures and they are sort of the conjunction between geometry and sounds waves.
Bards are - well -
could be spellcasters that, instead of using themselves or writings, use the patterns made by sound in order to retrace the leylines and channel their arcane energies.
Anyway, I am not advocating for bards to be implemented into the game. To be honest, their premise still strikes me as quite silly and I'm not sure they'd really fit WoW. That being said, this was just an idea that came to my mind this early morning. Bards may be silly but they
could totally work. Lorewise.