We propose a new receiver architecture for coherent detection in slotted optical packet switching rings with elastic (rate adaptive) optical transponders. Such rings are a candidate solution for future datacenter and metropolitan networks. The new receiver can detect more than a single packet per time slot and consequently has higher flexibility (translating into higher supported capacity, or, equivalently, lower end-to-end latency, or a combination or both), at the cost of a moderate increase in the transponder complexity and energyconsumption (less than 10%). We apply network plan- ning and traffic engineering simulation tools (which we validate on small examples using theoretical models) to quantify the increase in network capacity and latency reduction that can be achieved thanks to the use of the new receivers. Finally, we identify the stability problem of the insertion process in the rings with the coherentreceivers, and propose a polynomial network planning algorithm, for the case of fast-tunable transmitters. We evaluate the cost of enforcing the stability, in terms of the additional transponders needed, for the mentioned case.