Two suggestions have been proposed by smedland for improving the specification of ordinal models. I support both of these suggestions, and encourage OpenMx users to leave their feedback on these proposed changes.
Allow neighboring duplicate values to exist within a column of the thresholds matrix. CURRENT: a column must consist of strictly increasing values. CHANGE: a column must consist of non-decreasing values. Internally, neighboring duplicate values are collapsed into a single threshold.
In a FIML objective function, if thresholds are specified and expected means are not specified, then internally create an expected means vector of 0's. CURRENT: all FIML objectives require an expected means vector. CHANGE: FIML objectives with thresholds do not require means.
In addition to these two proposed changes by Sarah, I have two additional proposals of my own. These are intended to simplify the current interface.
Eliminate using NAs at the end of columns in the thresholds matrices. Contingent on proposal (1), use duplicate values to fill a column instead of NAs. Possibly use +Inf at the bottom of columns.
Eliminate the possibility of multiple threshold matrices. I find this interface confusing and prone to errors.