RIDE is already quite good. It is simple and effective and in a sense better than jupyter. Throw in some D3 they would get the graphical capabilities, just like how jhs does it.
I'm actually designing one better. :-) Probably a few years out from true production ready (maybe more, who am I kidding, probably more), but definition something cool.
A comercial example? Mathematica.
Imagine a Mathematica clone with APL...