Aha, I've been crosspicking for awhile without even knowing it! (But my left hand work is not as good as Ondrej here.) It just seemed like a natural way to transfer fingerpicking technique to flatpicking my ukes, banjo-uke, and banjo-mandolin.
I use this now on my soprano ukes, one tuned low-G and the other restrung with Aquila fifths for mandolin tuning. I am trying to apply this to my Kala KA6 six-string tenor uke but its strange setup, with the C and A doubled in octaves so the top course contains both the lowest and second-highest strings, is a challenge.
I use the thinnest possible picks on the ukes' composite strings, Jim Dunlop nylon 0.38mm. The strings should last longer this way.