FYI: I'm co-chair of the Math WG. I'm not an expert on W3C rules, but I'll do my best.

@mhchem: mmulticscripts is an area where MathML learned from TeX. I can't speak to what TexVC will do, but if there was some way to get the information that something is a chemical element (mhchem -> MathML output often puts things like "CO" into a single mi, so that needs to change) along with somehow tagging the whole \cd{...} as a chemical equation, that would at least tell AT that this mess is a chemical equation instead of forcing them to guess.

I don't think it changes anyone's plans, but please be aware that MathML 4 is adding an "intent" attribute to aid in speech generation. The MathML draft spec has some text, but it is still changing, so nothing needs to be done now. There will likely be some defined intent values related to chemistry that should be used when ce gets translated to MathML. Most likely these will be some "intent properties" such as "chemical-element" and maybe "chemical-formula" and "chemical-equation".

First off, thanks for the +1 for the reformed WG.

A few MathJax updates:

1. They have fixed the accessibility problems.
2. mhchem is supported in V3, although details have changed.
3. They just announced V3.0.5 saying they have enough confidence in it to officially announce V3 for general usage.

Just a warning that accessibility has changed considerably in V3. I filed a MathJax issue that has some discussion about the inaccessibility of V3 out of the box. If the output is to be accessible, MathML needs to be hidden as was done in V2 and is currently done on wikipedia pages. In V3, the way to include MathML is described here. MathJax may change it's defaults in some configurations based on the inaccessibility as V3 currently exists; definitely check the output for hidden MathML if you switch to V3.