Piwik::getPrettyNumber, which turns 1000000 into 1,000,000 or 1.000.000 should be used on every numeric value in Piwik to make report data more readable. I think this can be done by:
Should probably be done after widget integration testing is up and running.
Sounds like a good plan! Alternatively we could do it in a Smarty filter with a regex... but hoooking in datatatable is doable too (and yes, not in the API result)