Those old enough to remember the Stylophone (my brother had one) will recognise its modern equivalent, Pocket Miku. It's the same shape, the pattern of the 'keyboard' is much the same, it has the same kind of stylus attached by a similar short wire – but this gadget sings with Miku's voice – either the notes' sol-fa names or one of five preset lyrics.
You can listen either via the built-in speaker, or headphones/ear buds (I suspect something is supplied with the unit, but cannot be sure of this). As a product of the digital age, it also has a USB port.
If Pocket Miku were ever to be marketed outside of Japan (and perhaps its immediate neighbours), I wonder whether it would still have the kind of 'new fad' impact its precursor did all those decades ago.
I suspect we shall never be able to find out, but perhaps if some were bought 'over there' by western tourists and brought back to their own countries a demand might build to the point where it was irresistible. I suspect it'd need more than five songs and 'Do-Ray-Mi' to be in a version that could sell well here, but that's not difficult to implement.