Additionally, ECN is just between hosts, end to end. If an flow is not ECN enabled (neither of the ECN bits set), then the routing gear does what it always has done, drop a packet. Only if one of the ECN bits is already set (meaning the flow is ECN aware, end to end) does the router set the other bit to signal congestion. So enabling this on routing gear would have no impact on user traffic except to allow a better experience for ECN aware flows.
In other words, allowing this option in the network gear would have no impact on non-ECN flows and only help flows that negotiated ECN end-to-end at connection setup. These flows would already be known to be trouble-free for ECN else they wouldn't have been able to negotiate it.
