There's only 5 champions that use energy in the game though, which is an incredibly small niche to create something for. They're completely different classes as well, Akali is an AP assassin, Zed is an AD Assassin, Lee Sin is a Bruiser/AD Caster/Jungler, Shen is a tank, and Kennen is a mage. The only way you could really design an item that they'd all find useful is to make it overpowered or have interesting mechanics that make other champions jealous by merit of the item having useless stats. And no matter how you split the 5 champions picking it up it becomes problematic. Only being viable on 5 champions isn't a wide range of champions at all - regardless of how you look at the viability of things like Hydra, Hurricane, and Rageblade all of them can at least put everything to use on close to half the champions in the game. And if it was useful enough all 5 energy champions picked it up, it would likely feel like a requirement more than decent item choice. If any of them could overlook the item for other things it would generally be seen as underpowered and completely unnecessary.
I wouldn't call energy as an overlooked niche so much as a nightmare for design purposes.
Probably the best you could hope for is some item(s) offering bonus to resource management for all champions regardless of what resource they use (fury, heat, energy, health, nothing), as it could potentially be useful enough to merit adding, but even then you're probably not going to make it feel viable on all manaless champions. At least you have runes and masteries to effect energy as-is.