Hi Tamam,
At the moment there is no plan to include the possibility of dead times in the model. The easiest thing to do, which would lead to an equivalent closed-loop behavior is to eliminate x_{1} from the optimal control problem since it will not be a function of u_{0}, but of u_{-1}, which is known, and can hence be computed under the assumption of nominal dynamics. Then you can treat x_{1} as the initial state of the system in the modified optimal control problem. This all boils down to predicting x_{1} given the current control action and use it as initial state of the system.
This workaround should cover your case, if I am not mistaken 
Cheers,
Andrea