In fact, it's pretty easy to bodydrag upwind with an arm layed on the board, since the foil acts as a giant fin. With a Flysurfer it's even easier.
True - but you have to angle the board so the keel/mast is in line with the watersurface.
If you just put your arm over the board with mast straight down, you can not bodydrag, as you need at least 1½ meter of depth, preferably more, if you dont want to damage the foil on the bottom (assuming there is always up to ½m waves)
So you need to be able to bodydrag upwind and out with the board edges and wings acting as keels - which works fine, but many different ways of doing this.
The tricky point is of course when its 10 knots or less - as above 10 knots everyone can boarddrag upwind easily I assume.
But in light and super light winds, it becomes a real task and maybe not possible always ?
You might be able to ride in less wind, than you can body/board-drag - because the kite can not stay in the air by itself unless a special light wind kite of course.
This is why sideshore or sideon is preffered in really light conditions - as you will also need some downwind space for getting into planing - so bodydragging out in dead onshore can be really really hard, and you might end up hitting something while trying to foil, for riding in sub 10 knots
Thus, your board dragging out has to be able to get you well clear of the coast (far out) and very important to master in light conditions.