Consider an inventory system for a big box retailer. I can't think of anything better than a fat-ass RDBMS as the primary data store. Sharding sounds like a horrific idea. There are myriad workloads like this.
Personally, I've seen pgsql handle terabytes of data just fine and it wasn't really noteworthy or a source of problems to even bring up considering something else. YMMV but it's a good idea to use logic and reason to dictate architecture instead of following the shiny thing or hubris.