I'm not sure about website but for date, period and segment it should be quite easy to implement for Piwik 3.0+. I did a very quick POC here: https://github.com/piwik/piwik/commit/83ce9688be41d7521f1569708fd4e1e0e9a6d7b9
Pretty much the only thing that takes a bit of effort is to change the calendar and segment selector (and maybe website selector). So far the calendar selector never really closes as the page is just reloaded anyway. Instead we'd need to change the date selector, update the displayed date in the widget and tooltip, and update
piwik.period JS variables if needed. It's all feasible though.
Would improve user experience quite a bit by removing these page reloads. The widgets / reports would just reload instantly.
it would be a fantastic improvement to UI speed and would make Piwik user experience more enjoyable :+1: adding tentatively to 3.0.0
FYi: When pressing the back button the selectors need to adjust themselves to select correct segment / date / ...
I believe this is done by now