Just wanted to pop in regarding the lore evidence of healing spells being water-based, since it seems the idea was ditched.

This is taken from the level 5 conjurer quest:

As you yourself have witnessed, Sylphie possesses a natural talent for the conjury of mending and restoration. Alas, her gifts appear to have blinded her to the need for study, and she outright refuses to learn about the natural world. She knows nothing of the elements of earth and wind, and is quite incapable of conjuring even the tiniest pebble or the faintest breeze.
I had interpreted that bit as "healing is water", or at the very least, not earth or wind, since healing is all that Sylphie can do. Of course, since it's not outright stated, you are free to interpret it as you wish.

Either way, it doesn't seem like new water-based offensive spells are planned for now.