We have much lower traffic than that and our Piwik servers, with paid support from the Piwik team, often struggles to generate reports etc. Not convinced Piwik is that easy to scale.
People have scaled it to over a billion actions per month. No clue how much of that includes customizations though... It sounds way past the out of box limit.
Look at the comments from sandfox and afterlastangel in this thread. afterlastangel is pushing a billion, sandfox is around 300 MM per month.
I'm looking into replacing GA Premium ever since Easylist blocked GA tracking for Adblocked users and self-hosted Piwik seems like the best solution. I'd be well into the billions.
