It's promising, at least. I think a system like this would be the most useful if you're able to layer a query language on top of it, and apparently even FoundationDB (which had an SQL layer on top of a K/V store) didn't perform all that well. The Cockroach guys claim to have found a performant way of doing SQL on top of K/V, if I remember correctly, but we'll see. But having transactions in a distributed K/V store is certainly useful.