What does running their own data center have to do with it? As I understand it, this daemon could be deployed to a VM instance.

Great question! You only care about this if you care about cost utilization. If you don't care about cost then you will just statically pre-allocate the space on a host, waste the slack, and never overcommit. If you do care about cost then the pessimistic pre-allocation of space will look wasteful and you'll want something like this.

The other aspect of your question is about how "many of us" are working at places with huge datacenters. If you count up all the folks at Amazon, Google, Microsoft, Facebook, and Apple how does that compare to the long tail of people operating smaller datacenters at smaller companies?

OOM issues have arisen at every at-scale operation I've ever been involved in. OOM killer does its job, but this seems like it could make it even more manageable.

There are companies out there who prefer to be in control of their own data and core business, but their numbers are shrinking.