I don't even see why they can't make a spy banner brand flag, they already have the flag drawn. All they need to do is layer the navy blue color and put something spy related on the flag. I'm pretty sure something that simple can literally be added to the game in about five minutes. Devs are just not interested in what won't make money. I don't support tthis idea at all because making them the same flag would just show pure laziness.
No support. Lack of a banner is something people just have to deal with when choosing a mostly spy build.
This was promised when the banners first came out. As usual devs are unable to come through on promises. Spy banners and pvp being at the top of my list.