Could it be possible to impliment an Alliance Chat Tab?
There are several guilds that run with each other and an aliance chat can be useful. Also it could be handy for those large guilds that have "two" guilds to handle all their members, as well as those guild that have "feeder" guilds for lower levels.
Basically if you were forming for, say a raid, and you need to fill out the ranks, you can go to a "second" teir (guild chat being the "first" tier) by sending out a message over Alliance chat.
Also this will enable those who enjoy thier guild, but they belong to a small guild, and will expand thier network.
Guildleaders can do say /aliance invite "guildname", that will send an invite to the guildleader of the other guild. They can accept or deny. Gildleaders Can limit who can post or read to the aliance net, to only officers or all. And sent aliance messages will only goto your aliances, not you aliances' aliances.