I recently compared piwik with few other analytics Clicky vs Piwik | Clicky
I would like to suggest few of my ideas.
Piwik admin is kind of cluttered it sure needs a revamp - Suggestion: Bootstrap Admin Templates | WrapBootstrap
atleast make the piwik software to be able to install these themes as plugins without the need of much coding expertise.
Add User Management module into the software because there are a lot of uses in it.
Piwik can serve as a platform for both analytics and as adserver
Ecommerce Cart Plugin will be a great addition to the software - A merchant using piwik for the ecommerce server analytics if they can use the Ecommerce Cart module from piwik it will serve a better analytic tool to track conversions
Heat maps is verymuch required
and visitor prediction analytics based on their earlier behavior analytics would be a great tool
IMO, Piwik should offer two products
1.Piwik Business Intelligence Tool
2.Piwik ECommerce Intelligence Tool
3.Piwik User Intelligence Tool