The third version of the 'FBC' package has been worked on for the last few years, with discussion happening both in the FBC working group, and in the sbml-specifications issue tracker:
A version of the spec was submitted to the SBML Editors, who have individually signed off on it, and now formally present it to the SBML community for one final round of comments and suggestions:
If you have any interest in FBC modeling, please use the next two weeks to peruse the specification and report any issues you might have on the sbml-specifications github issue tracker, or by posting here to the sbml-discuss mailing list.
Thank you!
-Lucian Smith
on behalf of the SBML Editors