With the sudden outpouring of lots of plastic ukes in the past couple of years I'm surprised no one has done a plastic sopranino yet. The sell of plastic is for durable portability...
I found a video of a 50's plastic sopranino being played here:
UKulelezaza is impeccable! That is the iconic plastic ukulele video, for sure. (note: at least a dozen of the views on the view count are from me, over the years).
I love ukes, but would never buy a plastic sopranino. I think the uke is "toy-ish" enough at my preferred size of soprano.