Ah, that's a very succinct reason. Because my needs are somewhat ordinary, I often forget about the notion that columns might be anything other than vectors containing single values. I wonder if some of the more complex datatypes could be added to SQLite in the same sort of way that Spatialite has added geospatial geometries as column types. In fact, I wonder if some of those geospatial types might be abused to push past the 90% use case barrier.

Hmm... Now I'm wondering what level of extension to SQLite would be required to create a shared library that could be plugged in to any of the various languages that need dataframe functionality. DataLite?