Hi.
Gradient mesh is a "feature in development", so to say. It is not yet part of the curent svg specs, so other programs won't be able/refuse to implement such a feature. (The flowed text is another similar feature.) On top of that, it' not atotal guarantee that word would support every feature of the svg specs -like, most probably they won't bother much with filters -don't know, haven't tested.
Tavmjong Bah implemented the mesh gradient in inkscape, and also he is part of the svg workgroup.
Not sure about its current state although can recall it is sheduled in a later version.
Some related reading on the mesh gradient can be found
here.
