This is a topic we have discussed quite a few times by now, and it's bit of a tossup between having the icon change to match your damage type (like Lightning Fireball not having icon looking like a Fireball, but more like a plasma or lightning infused fireball).
It does come up with a downside of newer players not being able to recognize skills they see in guides or by content creators because the icon doesn't match any of the skills they can see when they open the skill's page. It's also a lot of extra art work.
There's a certain threshold where too much icon modification might actually become a detriment and a lot of wasted work instead, such as from Fireball (1 fire projectile icon) to fully converted lightning Fireball that shoots multiple projectiles, be it in a sequence or not (lightning Fireball icon with several projectiles in it, arranged based on behavior).
Personally I would love to see this one day, but it would likely be just based on damage type and not other aspects...
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