This is very much proof of concept code, and I don't intend to actually build this. So if you want to use this, expect to contribute all the work yourself.
I always have to google which characters to use when doing date formats
<?php
echo $date->format("Y-m-d\TH:i:sO");
So what if I didn't have to?
<?php
$format = (new DateFormat)
->year()->dash()->month()->dash()->day()
->raw("\T")
->hours()->colon()->minutes()->colon()->seconds()
->diffToUTCInHours();
echo $format($date); // 2019-02-07T10:25:55+0100
);
There are some more examples in the tests.
You could do all kinds of fun stuff like $format->->month()->long()->space()->quote()->year()->twoDigits() to get January '19, but that hasn't been implemented.