The ESODirect showcase of the upcoming subclassing system, which in my opinion will destroy class identity and the little endgame build diversity left, has inspired me to a much more interesting approach to subclassing which would not only keep class identity but would also expand on it. Give me your opinion on it!
Note: this is a very quick brainstormy draft of how a good subclassing system could work in ESO. Also, I am not a native English speaker, so please excuse eventual errors.

Basic Idea: Each subclass follows a theme that is somewhat related to the original main class but distinct from it. To achieve this, every subclass keeps two skill lines from the main class (at least in function) but replaces a third one with an entirely new skill line. In the following are examples of how this could work in practice.

The simplest and easiest way to implement this concept would be to stay close to the main class and keep two skill lines entirely unchanged. One example could be the “Bloodknight” subclass of the Dragonknight:

Bloodknight
Summary: The Bloodknight has left fire and poison behind to eviscerate his adversaries and revel in their blood.
Skill lines:
- Carnage (NEW): entirely new skill line focused on bleed damage. Some skills eviscerate the enemy, making them bleed, while others use blood itself to deal damage.
- Draconic Power: unchanged
- Earthen Heart: unchanged

An intermediate way that would keep the workload on implementing this system low but gives a more unique identity, would be to keep the theme and base animations the same, but alter color and effects similar to the skill styles that are already in game as well as the names, if need be. One example could be the “Dark Templar” subclass of the Templar:

Dark Templar
Summary: The Dark Templar has turned away from the path of the light and searches for everlasting darkness instead.
Skill lines:
- Daedric Spear (Renamed from Aedric Spear): animations unchanged, but with a darker, maybe bluish color scheme and adjusted names.
- Dusks Wrath (Renamed from Dawns Wrath): animations unchanged, but with less light centered names and color scheme.
- Devouring Darkness (NEW): entirely new support-focused skill line, possibly with some damage dealing skills.

Another way to implement this system would be to pay direct attention to creating new class identities. This would be more work for the devs, because many skills would require new animations. One example I came up with, would be the “Grovekeeper” subclass of the Warden.

Grovekeeper
Summary: The Grovekeeper is no longer utilizing animal companions or frost magic but has instead devoted himself to healing the nature and spreading wild growth everywhere he treads.
Skill lines:
- Inexorable Overgrowth (NEW): damage focused skill line that centers around thorny, tentacle-like vines.
- Green Balance: mostly unchanged
- Nature’s Reclaim (Renamed from Winter’s Embrace): functionally unchanged but new animations and skill names that fit to a plant/nature-based theme.

Obviously multiple subclasses for the same main class are possible. Two ideas that go into entirely different directions would be the subclasses “Foreststalker” and “Voidwalker” of the Nightblade.

Foreststalker
Summary: The Foreststalker dwells in the dense forests of Tamriel, stalking in the thicket for his victims.
Skill lines:
- Assassination: mostly unchanged
- Pathfinder (NEW): entirely new tanking and support focused skill line with a theme that centers around survival in a hostile (nature) environment.
- Mend Nature (Renamed from Siphoning): functionally unchanged but with animations and skill names that fit better to the nature theme of the subclass.

Voidwalker
Summary: The Voidwalker harnesses the power of the void to conjure shadows and to siphon the life essence of its foes.
Skill lines:
- Endless Void (NEW): entirely new skill line that utilizes void-themed skills to deal damage.
- Shadow: mostly unchanged
- Siphoning: mostly unchanged

Other ideas I came up with are:
- “Tidemaster” from Sorcerer: Replaces Deadric Summoning with the ocean-centered "Tide Mastery" skill line.
- “Plaguebearer” from Necromancer: Replaces Grave Lord with the disease damage focused “Harbinger of Pestilence” skill line.
- “Crystalformer” from Arcanist: Replaces Herald of the Tome with the damage-oriented "Lacerating Crystals" skill line and renames Curative Runeforms to Curative Gem Power and Soldier of Apocrypha to Crystallization along with altered animations.

Please leave some feedback and your own ideas how the subclassing system could be improved.