Confidence intervals are basic to most results sections now, so implementing Mx's 'Intervals' likelihood-based confidence intervals (Neale & Miller, 1997) (plus standard error-based CIs for speed) would be high on the wish-list
maybe something like
mxInterval(..., percent=95, type="ML") where ... consists of matrix addresses
mxInterval(z.A) would mean all cells of A
mxInterval(z.A[1:2,], type="SE") first two rows of A, standard-error based method