I could see this feature to be worth something to someone. But before I would use it I'd find someone to build me a SAN RAID unit based on Solid State Disks with a disk fail system.

I have been burned by one too many UPS/Generator/Switch failure in the past to trust data to plain old volatile RAM.

This is a Mongo DB Is Web Scale solution. As an eBay/Amazon/Google use yes. But they have the money to do triple redundancy failover solutions. Most of us aren't at that scale.