The amount of data that gets sent around when in an alliance today makes it problematic, it works if it's a load of casual players but if you are in an alliance of min/maxers it will be hellish.
The only way they could make this work would be to allow alliances to queue, but break them into 3 groups inside as with Omen or something. Or people to communicate in chat still but remove all the alliance ui stuff.
When you have 3 parties, and half of them or more are using gearswap to constantly change gear for every possible reason the amount of UI HP/MP updates being sent to everyone is insanity, which normally would not matter but when you run a game with 56k cap it does.
Either that or just add a ui option to hide block data being sent about mp bars of anyone outside your party at a bare minimum or something.
Make a video of an alliance with a lot of people using GS and their hp and mp bars are constantly bouncing around, and every single change from every single player is sent to everyone's client every second.
Try Dyna D with a group of casual players in an alliance and then try it with a load of people using gearswap, and awe at the lag as the connection gets congested.