OMDoc1.3 is an incremental extension of OMDoc1.2 that addresses immediate needs from the OMDoc applications that have been the focus of development in the last years.
In a nutshell, we have the following changes now (see a [report:11 full list of what is under discussion]; the OMDoc1.3 Draft Specification already documents some of them).
The work on OMDoc1.3 is public, the changes are reflected in the draft OMDoc1.3 specification . Upcoming changes are discussed as GitHub tickets with the [milestone:OMDoc1.3 OMDoc1.3 milestone]; see the [report:11 open issues]. If you are interested in participating in the discussion, please feel free to add yourselves to the cc fields of the respective issues.