This could be eg added to Visitor - Software - Plugins. It could be possibly even done in a plugin. I reckon for many websites it would be useful to know how many visitors have an ad block installed.
An ad blocker should be only detected and tracked, there should be no warning etc.
That would be very helpful considering that uBlock Origin, Ad Block and Ad Block Plus have been installed more than 22 million times on Chrome alone...
Problem is that, when there is an adblocker, likely Piwik will be blocked as well, so the numbers will be highly inacurrate?
It depends. Eg we're not blocked by Adblock Plus by default but partially this is true for sure. In such a case people would need to "Whitelabel"
See http://www.kaushik.net/avinash/adblock-tracking-google-analytics-code-metrics-reports/ and re whether Piwik will be blocked as well http://www.kaushik.net/avinash/adblock-tracking-google-analytics-code-metrics-reports/#comment-1056775
Basically it still gives you more insights then not tracking it.
Can be easily achieved with custom dimensions / custom variables / events or a plugin (easy to develop). We could test it on our own site at some point to see what the numbers are
Any request containing "piwik" is blocked by uBlock Origin.
I actually had to disable uBlock to write these comments.