Maybe the answer is right in front of us? Runes are so easy to swap, what if they add some rune slots to our rings/trinkets that are all defensive-related and have flavor? That way they can be class-specific and have an extra layer of appropriate balance. They are easy to swap, unlike talents, and give more discovery. Yay!
I don’t know if it would be best to limit the runes to PvP or just f* it, do it live, because Discovery is a sandbox of fun anyway.
Here is a feeble attempt at some examples:
-Rune of Prismatic Cloaking: Mage-Ring / Castable in addition to other armors, damage received from spells increase your resistances to damage from that school by 5 (DoT ticks by 1). Melee attacks received increase your armor by 15. Each effect stacks up to 5 times your level. When the maximum stack of either is reached the cloak breaks and must be recast.
-Rune of Ethereal Phasing: Mage-Ring / When interrupted in combat, chance to refresh the cooldown of blink, make the next cast cost no mana, and grant invisibility for 4 seconds.
-Rune of Chronostitching: Mage-Trinket / Damage from enemies that would reduce your health below 0 instead reduces your health to 1, but is instead stored into a chronostitched mana barrier. The next spell you cast causes this barrier to explode, dividing the damage among yourself and all enemies and allies in a 5 yd radius.
-Rune of Rapid Retreat: Warrior-Ring / 5 Rage, Shout to command yourself and nearby allies 45% movement speed and reduce the chance they are hit by spells and attacks by 5% for 10 sec. Any damage you or your allies do remove this effect.
-Rune of the Shrugging Stoic: Warrior-Ring / Shrug off Damage over Time effects, reducing damage received by them by 50% for 15 sec. 45 second cooldown.
-Rune of the Persistent Gladiator: Warrior-Trinket / The threat of death energizes you. Automatically charge to the character who would deliver a killing blow to you and enter a bloodthirsty rage. You heal for 20% of your base health and become immune to all damage but can only use melee attacks and slam/shield slam until the rage ends. Lasts 10 seconds, 2 minute cooldown.
Cloak of Shadows for rogue would do the trick.
Survivability is great, offer some in these runes. However, I think what players truly crave is the ability to maneuver around death for a little longer.
Also, give mages Nether Tempest and let it bounce between both allies and enemies, when it hits an ally it heals, when it hits an enemy it does damage.