Aggregations and the like require sequential access, but random access is very valuable for RDBMS where in most cases the vast majority of operations are random (write a record, pull a record, update an index, etc). Many of the systems in play have an extraordinary number of optimizations for sequential access -- assuming terrible random access -- but would still hugely benefit from something like this.
However those who say it obsoletes anything beyond the most trivial of KV stores are way off the mark. It's a possible optimization for all sorts of database systems, certainly including RDBMS systems (many of which are layered over a KV store or sorts). There are disk systems for Oracle DBs that can run a subset of SQL right at the storage later, filtering by predicates, doing index searches, etc.
However those who say it obsoletes anything beyond the most trivial of KV stores are way off the mark. It's a possible optimization for all sorts of database systems, certainly including RDBMS systems (many of which are layered over a KV store or sorts). There are disk systems for Oracle DBs that can run a subset of SQL right at the storage later, filtering by predicates, doing index searches, etc.