Are there any comparisons between fractal trees and the database cracking/adaptive indices advocated by [1]? It seems like they're going after the same use pattern but cracking is relatively simpler and even faster for inserts.
An interesting new development is http://getkudu.io/ which applies some ideas common with Fractal Trees and other write-optimized data structures (like LSM-trees) to column stores.
At Tokutek, we had some designs for how to implement column store-like data models on Fractal Trees (we called them "matrix stores" because they had some of the benefits of both row stores and column stores), but we didn't get around to implementing them.