Honestly, scrap the old armor upgrade items and gold cost all together. Let us upgrade it similar to how we upgrade our valor / conquest gear, but we use Timewarped Badge’'s instead.
Would have to have more ways for us to aquire Timewarped Badges of course, so i’d like for the old world quests in Legion, BFA, SL and eventually Dragonlands reward these badges.
Also, introduce leveling dailies or quests that reward these badges while a new player levels and introduce them to the heirloom vendors and what they do.
This will benefit vets of the game and new players alike!