As of now, there are none aside from Essence Reaver, which is crit reliant, and Manamune, which is honestly kind of poor for mana regeneration. Would there be a downside to creating a Morellonomicon or Athene's for AD? Maybe like 50-60 AD, some CDR and mana regen?
ADs don't really need mana regen. Those that do are in 3 categories: tanks that build flat mana (rare), ADCs with crit building Essence Reaver, or the 2 or 3 champions who build manamune
and others) to just abuse their power even more.no
because the AD champions that are mana hungry AND don't invest in mana are assassins. 
and these champions should not ever be given an item for regen or mana that they don't need to make a tradeoff for
