1. It would be nice if a manufacturer (Mocke?) started making pfd's specifically for LD ski paddling. For example, my Lotus pfd is pretty minimal as far as pfd's go, but it's made so darn bombproof (with whitewater paddling in mind), that it's stiffer and heavier, and hotter than it needs to be. We really just need something pretty simple and not made with 1000 lb test cordura and kevlar weaved into the fabric, right? If it were super lightweight, flexible, had ventilation holes, I'd wear it all the time. Look at the revolution in bicycle helmets. That's what I'm talking about.
2. I occasionally use an inflatable pfd. But, I don't like to have to rely on something that I have to fiddle with and inflate when I really need it. That said, the manually inflatable ones are pretty good, though - by manually inflatable, I'm talking about the CO2 inflatable pfds that don't automatically inflate when they get wet.
3. If an LD ski race stays within a short distance (500 m?, 1 km?) of shore, then I can see very good reason to NOT require paddlers to wear a pfd as it makes little sense to do so. But, if a course takes paddlers more than a specified distance from shore (2 km?, 10 km?), I can certainly see the point in making the paddlers wear their pfd.
As an aside, I occasionally do local races on shallow, very slow flowing rivers or lakes that are so narrow you could throw a rock across them, and wearing your pfd is often required. That makes no sense.