I have read many of the posts around using non-SQL databases for Piwik. It does not seem like anyone is taking the lead on such a project - and I get the feeling that it would be a significant project to migrate all of Piwik to a non-sql environment.
We are talking about an idea where we move the piwik_log_action, piwik_log_visit and piwik_log_link_visit_action tables onto a MongoDB server, while keeping all of the rest in MySQL.
If we are able to change the tracking script to insert into MongoDB and develop a Piwik plug-in that could do all the redirection of queries from Piwic on these tables to the MongoDB we could potentially have moved the most sensitive parts of the equation away from MySQL. These tables are responsible for the vast majority of the DB storage needs and the massive amount of inserts. All archived data would be preserved in MySQL - so all reporting but LiveVisits should be untouched.
Have anybody tried anything in this direction?