MathML is a valid compile target for TeX equations, it doesn't matter how easy it is to write by hand nor does it matter how verbose it is. It is intended to be an interchange format seldom seen by human eyes or written by human authors.
When the OP says "if scientists have an easy way of creating markup versions of their LaTeX files" it sounds like they'll be writing it by hand, don't you think? Alternatively, a toolchain involving compilation to HTML+MathML doesn't sound to me like a problem for browser vendors.