Mage item changes - thoughts?

Before getting into the meat of what I'm thinking - I wanna say, I do, overall, like the changes made with the AP items. I can say this because when I saw them, I immediately started thinking of how to use them and who best synergized with what. I like the interesting styles each item inspires and the interactions and possibilities.

But there is one thing that worries me that kind of died with the old Morellonomicon; I still don't understand how mages are supposed to sustain mana anymore. It seems that unless your jungler's always giving you blue or you're taking Manaflow Band, you'll always run out of mana sooner or later. This is fine early and mid-game IMO, but late-game it's often the case that I'm outside of the base for a long time and don't back for a long time. For ADCs, this is not a problem, because of Essence Reaver, but for mages, you don't have a way to sustain your mana - you just have to either manage it by not casting spells, which I would think reduces your threat level, take blue buff, which is temporary, or you have to build RoA? But some mages, like Xerath or Ziggs, don't want to be in range to take damage and sustain their mana with RoA. They are mages who literally want to stand in the back and spam spells - and while Manaflow Band helps, it doesn't solve the issue entirely. In a way, these new items are really powerful, but they also lack a key way to restore the resources needed to make use of their stats. Kinda drives me nuts; I don't know what Riot was thinking. Sure Morello's was too much of a multipurpose item, but that passive mana restore was huge, and not replacing it in one way or another seems kind of nuts to me.

By no means am I an expert, but I wanna hear what everyone else thinks about this.