I think it needs a new mid-tier item that builds out of Pickaxe + Faerie Charm. That way AD champs that have early mana problems could build the new item, then get their essential items, then come back and upgrade to Essence Reaver.
Essence Reaver actually has nice stats, but all the champs that could use it will prioritize a different first item, then either penetration or tanky items. By the time they build Essence Reaver as a 4th-6th item, they won't need the mana regen, so they'll take something else with a more useful passive/active.
For example, I love the stats on Fiora, but I always build Ravenous first, then usually a penetration item. I could grab a BF Sword or VS next, but when it comes time to build it into Essence Reaver, I'd rather have the extra LS from Bloodthirster or the extra AS + passive/active from BORK. If I could go Ravenous --> AD/mana regen mid item --> penetration item, then I could justify taking Essence Reaver.