Also different buffer scheduling mechanisms can be used. There will certainly be a difference in the performance of the nodes, but the standard should leave freedom as much as possible. No special configuration should be mandatory. Equipment manufactures and network operators should decide.
Preemption is less complex than is claimed in all email-responses.
Also preemption should in fact remain a degree of freedom. Nodes with and without preemption can perfectly exist in the same ring, if the ring input-part of each node can handle preempted packets so that preempted and preempting packets are received correctly. In that case, a preemptive node will not use the feature when the next node is not preemptive. Again equipment manufactures and network operators should be able to decide whether it will be necessary to have packet preemption or not. Here, voice-like applications and large data frames ask for preemption.