Well, I just recently posted in another forum the idea of what ESO might look like, without a "Class" system at all (more like traditional Elder Scrolls games). But considering that's a pretty radical idea, I feel like maybe these ideas would be more realistic!
First off, I love the idea of playing just a normal "Adventurer" sort of character. Essentially more of a treasure hunter, with skill-trees that maybe focus on traps (damage), raw athleticism (tanking), and perhaps a very vague, almost novice sort of "magic", like someone with latent magical talent but just kind of bumbling their way through. Almost more like "telekinesis" or "psychic power" than the usual elemental magic.
Secondly, a proper elementalist "Mage". Ideally, they would focus on Frost, Flame, and Shock abilities, with Magicka-DPS options in all three trees, with other utility within (ie. Frost having some tanky abilities, Flame offering some healing, and perhaps Shock offering Stamina or Melee-oriented skills). My thinking here is that, even if you can still play them as a brute-force warrior, or as a pickpocketing thief, I like the idea of a character who is just "broadly magical" in nature, who can apply a little magic to everything they do.
Just my two cents. Personally, just none of the current Class options quite "connect" with me. A lot of them feel like they veer a little too "evil" (or the Templar, which veers almost too "holy"), and I really just want to be able to experience the game and all its regions as a broad "Adventurer". And like I said, even if going the route of a "Mage" style class, it still leaves it broad enough, I feel like the character is truly mine, and not predisposed to have a certain background or personality type.