In the Grey Mountains endgame (120, Update 23), embers are the new Ash. You can barter them for boxes with your choices of gear in them. Exactly what's in those boxes I personally don't yet know, but hope to soon.
For your reference, here is a list of ways you can acquire embers. Please let me know if I'm missing a way:
[list][*]Opening Adventurer's Lootboxes. This requires a steel black key, saved from pre-update or purchased from LOTRO store.
[*]Crafting quest: bestowed by Mozhek in Skarhald; rewards 1,000 embers but requires 7 dwarrowgleam shards
[*]Quartermaster quest: 25 marks of the Longbeards can be turned in weekly for 500 embers if you are under level 120, or 1000 if you are at cap.
[*]Reclaiming the Grey: quest, auto-bestowed; quest has 3 tiers which each require completing 20 quests in the 4 resource instances. Each tier bestows 500 embers, and the quest resets to tier 1 weekly.
[*]Fight for the Grey: quest, auto-bestowed; complete each Grey Mountains instance on size 3 or 6 weekly; rewards 750 embers
[*]Final boss chests: the final boss chest in each instance will have embers in it on the group versions (2/3/6); higher tiers reward more embers, based on the type of chest and if you have favored pulls left
Hope this helps!