Just saw the update in phabricator, and think it is somewhat odd declare that this is of limited use when technically date elements are more used in pages than many other elements. Statistically speaking, dates are are more used than gimmicks like graph, score, unnecessary signatures, and many other non-essential features especially in a so-called encyclopedia.
Making this tool is trivial, and all one needs is userscript that either inserts a link to the toolbar, a button in the insert drop down, or even just a keyboard shortcut that does something like:
<pre>
var date = (new Date()).toJSON();
var fragment = surfaceModel.getLinearFragment(rangeToRemove);
var frmTimestamp = jsonDate.substring(0, 10);
fragment.insertContent(frmTimestamp);
</pre>
A more complex tool / experience may indeed take a bit more time and research. But frankly there are plenty of libraries that do this effortlessly.
Anyway, thanks for adding the suggestion to phabricator (Don't shoot the messenger as they say).