Sorry to disagree, but I think you are misunderstanding how traffic shaping works.
It can be handled only on red interfaces.
From shorewall manual ( http://shorewall.net/simple_traffic_shaping.html ):
Simple Traffic Shaping is only appropriate on interfaces where output queuing occurs. As a consequence, you usually only use it on extermal interfaces.
Still, we can implement what you are asking for, but it should be done in a different way. We can extended the "Address rules" tab inside the "Traffic shaping" page by allowing the creation of rules based on CIDR objects.
Regarding the pull request by @Nas, probably the part about VLAN can be accepted (but it should be tested if Shorewall complains about it); sadly, the blue part should be removed.