The onion packets in Lightning, as described in BOLT 4, include
short_channel_id's of the channels along the route constructed by the sender. But according to the same spec, the forwarding is non-strict, meaning that if the payment is meant to be forwarded from an intermediary node X to an intermediary node Y, X is free to choose any of the channels between itself and Y (a pair of nodes may have multiple channels).
short_channel_id's in onion packets excessive? Could we just specify a list of nodes along the suggested route and let each node choose the best channel to the next one?