As it stands now, to purchase the MaxMind GeoCity data is quite expensive ($370, then $90/month). However, they have affordable plans if you just want to use API calls ($20 for 50,000 calls I believe). Are there any plans to supply Piwik with a MaxMind API user/key to use this service?
http://dev.maxmind.com/geoip/geoip2/web-services
http://dev.maxmind.com/geoip/geoip2/web-services