After learning there will be more mythic items in the future, i took the liberty to create my own concepts for possible future mythic items, have a look for yourselves!

Ring of Namira
Enchantment - Reduce feat cost
Trait - Healthy
Effect - Gain a synergy to use on corpses in front of you to heal 3000 health
over 3 seconds, after consuming the corpse you gain Major Defile and 600 stamina recovery for 20 seconds
Bloodworm Helm
Slot - Head
Heavy
Enchantment - Fortify Magicka
Trait - Divines
Effect - Any ability you cast that's a timed summon allows to have one more of that summon,
while equipped you take 25% more damage from all sources.
Necromancer's Amulet
Enchantment - Reduce spell cost
Trait - Infused
Effect - Increases the duration of all timed summons by 5 seconds and increases the amount of damage they deal
by 30% but your magicka recovery is reduced by 50%
Umbra
Slot - One Handed
Sword
Enchantment - Oblivion damage
Trait - Nirnhoned
Effect - Restore 1000 magicka or stamina whenever you kill an enemy depending on which
resource is higher, everytime you kill an enemy your weapon damage is increased by 10% for 2 minutes
(Maximum 50%) but you also take 5% more damage from all sources with each kill (Maximum 25%)