@Meddler: What are your thoughts on a support item that restores allies' mana?

Since Soraka's rework, we presently lack any means of giving an ally a small mana booster when they need it (except for Clarity, which isn't viable). It's a real pain when your team's tank goes OOM in a fight because he/she can't build mana regeneration, and even a Frozen Heart or Iceborn Gauntlet can only increase capacity, not let you recover after you run dry.

A long time ago, we had an item called Mana Manipulator, which provided an aura of mana regeneration. It was removed because it could be bought right off the bat and made bot-lane harass compositions (i.e. Sona+Ezreal) and infinite-heal Champions like Soraka oppressive, while having little-to-no impact beyond early-game even in high-tier items. Now that regeneration bonuses are based off base regeneration, I think re-introducing an item with a mana regeneration aura would be particularly useful for sieging and extended fights.

I'd like to know what your thoughts are about a late-game item that lets you help your teammate's mana supply. Is it something that might be good to introduce? Or is mana regeneration/maintenance supposed to be up to the player from now on and not up to allies?