PostgreSQL has a somewhat similar philosophy of extensibility and moving things out of core. Consider something like PostGIS: it's an entire first-class geospatial system done entirely as an extension (I don't think any other database can claim that).
It's still basically a batteries-included distribution, but it is very extensible and getting more so. I expect to see many more domain-specific extensions (you can already see a lot at http://pgxn.org ).
However, I will say that it should be a simple core but not too simplistic. Especially for something like a database, some things are better done in the core (perhaps not inherently, but it's in research-project territory). That's really the challenge: it's not "pro-modularity" versus "anti-modularity"; it's about what constitutes a good base from which to build.
It's still basically a batteries-included distribution, but it is very extensible and getting more so. I expect to see many more domain-specific extensions (you can already see a lot at http://pgxn.org ).
However, I will say that it should be a simple core but not too simplistic. Especially for something like a database, some things are better done in the core (perhaps not inherently, but it's in research-project territory). That's really the challenge: it's not "pro-modularity" versus "anti-modularity"; it's about what constitutes a good base from which to build.