There are already a lot of spells (or spell effects) in the game that could be considered natural/druidish.
Oak/Iron/Stone Flesh
Summon Atronach as Summon Elementals
Charm/Command Animal or Kyne's Peace
Conjure Familiar (this could be improved upon by having greater level familiars, sabrecat, bear, etc)
Fire/Frost/Lightning Storm
Detect life
Call lightning
Clear skies
Calm
Courage
Waterbreathing
I'm sure there are a few others. There could be more spells that fit with the lore, such as spells that were in Oblivion/Morrowind. So it's not like it's IMPOSSIBLE to play a druid character.
Mods make it more than possible, especially if they tapped into things like summon spriggans, or insect swarm spells that spriggans have, etc.
This. What better "class" to summon forth a blizzard than a Druid/Shaman type character. Don't have to make a new school for nature magic either. Damage nature spells would fit in Destruction, A vines/earth spell that immobilized would go under alteration. Various summons, as mentioned already, like Spriggans would go under Conjuration.
In the end, I don't know if I really care if they added it. I don't feel like I need the magic system to be like D&D or other traditional "fantasy" games. And there is enough to RP a Druid already with imagination.