It's not scalable, but as an existence proof of what you're saying, my partner and I fulfill this role for each other - we each are tasked with remembering different facets of our lives (e.g. I know the plot and cast of every movie we've ever watched, she remembers to pay taxes :).

It seems pretty obvious we're heading for that utopia/dystopia where everyone is assigned a personal assistant loaded onto a pervasive mesh (your glasses, watch, phone, computer, desk, house). On the one hand it sounds great to have an AI assistant that knows what I know, a model of how I think, and the ability to fill in the gaps instantly. On the other, it's so ripe for abuse/deepening inequality, the idea almost qualifies as "don't create the torment nexus".