I am pleased to announce (preliminary) support for embedding mathml
files as ODF formulae in odt documents.

Specfically if one provides a link to mathml files as shown below

[[./equation.mathml]]

then the contents of the mathml file is embedded in the exported ODT
document as a ODF formula.

I intend to support link to *.odf files as well. (But this is not
available yet).

Moot point: I am still uncertain how the mathml equations specified in
Org format. For example, does the current approach of using file links
of the form *.mathml (or *.odf) extension sound OK? Should I use a new
mathml:// link type?

Please see the attached Org file for a quick demonstration of what the
current set of changes mean.

1. Update work area
2. Copy mathml.org, formula1.mathml, formula2.mathml to the same
   directory
3. Use C-c C-e O to export.

Currently the equations are embedded as unnumbered, display/paragraph
types.  

IMPORTANT: I am following this mail with a patch to org.el which will
add support for LaTeX-to-MathML conversion using an external
converter.