It allows queing downlinks, just as feeding multiple servers directly does.
What’s missing is any resolution of conflict - someone loses.
Actual conflict resolution would look at the gateways available to transmit the conflicting downlinks and try to assign them so that both get sent.
Or failing that, learn that the requested gateway is unavailable in time for the losing network server to try any others in range.
But the combination of TTN + packet broker hasn’t been designed to do that.