I wondered if the ebtables lines could be setup automatically like if there are two bridged interaces and web proxy activated. But I think it's not possible because NethServer is very flexible with bridging and networking, so autodetecting bridge mode will not work.
On some other firewalls bridge(transparent) or routing(NAT) mode is a very basic setting. I changed a FortiGate last week from transparent to NAT mode and it kicked away some interface, policy and rule settings. They seem to set up on the mode.
I really like bridge mode setup possibility, because one may use Nethserver as a firewall without changing other network devices but I searched the forum and did not find much threads about bridged mode so maybe a custom template is enough for now?
If not I'd like an option in advanced options so sysadmins are warned that it's an "I know what I do" option. It may be greyed out until two interfaces in a bridge exist.
Besides I don't know if we will need some special vpn configs if using bridged mode.