I don't know how extensive Unicode math symbols are, but it's unclear to me how you would display things like matrices and do alignment of multiline equations.
I'm not sure either. But I know that you can do crazy things with unicode, and I'd bet that if you treated treated unicode as a sort of low-level compile-to target you could then design a high-level language from which to write math text. I'm not sure of the practical benefit and maybe this would be even more inaccessible to people... but still, I think JS is great, but wouldn't pure HTML and encodings be even cooler?