I certainly wouldn't recommend anyone start with a special-purpose DBMS. General-purpose DBMSes will get you quite far indeed. (They got my data API company to

I certainly wouldn't recommend anyone start with a special-purpose DBMS. General-purpose DBMSes will get you quite far indeed. (They got my data API company to millions in ARR!) But when you hit a certain scale, and your general-purpose DBMS starts to struggle with things like "delivering millions of sub-1ms reads per second", and you start to look at what would be required to scale horizontally to thousands of elastic nodes with low start-up times and good QoS while serving your 100s-of-TBs dataset... you might just start Greenspunning something. Something that you might not at first realize is a domain-specific DBMS. But, once you do realize that, you may wonder whether someone has already done it better. And that (rather small) set of people, are the intended customers of a domain-specific DBMS.