It’s actually very easy to make a brush like this. You just need to adjust both the “elliptic” settings in the basic category.
But, yes, changing the angle on the fly with keyboard is not possible for now, it seems.
In the “classic” brush set is a brush named Calligraphy (not sure if this is a brush pack that comes with myPaint by default though…). I got one in my “Dirty” brush pack, too.
