Reading the original post I believe that the poster is expecting all the vlan interfaces being run in IPFire via one green NIC, presumably so that different firewall rules can be assigned to each of the different greenX zones.
This would require re-writing of the iptables and ipset code to work with multiple green interfaces.
Also all the WUI pages that have perl code dealing with the green zone would need to be re-written to include multiple green zones.
Any changes made to IPFire must always be able to function with all existing installations.
However the requested change would end up touching the two core functions of IPFire, Networking and Firewalling, and I believe the chances of ending up with changes that result in breaking existing systems with an upgrade would be high, due to the number of changes needed at the same time.
This is why IPFire-3.x is a fresh start development. No historical structure to have to take account of. Networking, Firewalling and Routing are all able to be constructed to work with multiple interfaces and zones that can be defined as users desire right from the start.