I also wonder what limitations you get on queries. Cause in Spanner, there's something about cross-directory queries, or Citus can't do cross-shard FKs iirc. There's no magic way to shard a relational DB, you have to deal with it one way or another.
Cockroach really doesn’t have limitations when it comes to queries. It is kinda magic in that regard. The single partition queries are the special case and are treated as rare. Cockroach ranges are quite small compared to other systems (~256MiB).
Interesting, I'll have to try it out at some point.