Unlike some of Apple's other features, UI, Apps, and operating software, Siri is not something that will be easy to improve. Siri represents the cumulative efforts of decades of computer science research by numerous public and private entities.

While it's easy to add more voice actions, making advances on the underlying technologies will require additional decades of hard computer science research. Apple, having no R&D division, will not likely even contribute to this.

Unless your main complaint is a lack of canned question types that it can answer, you won't likely see the fast improvements you are expecting in the next few years.