I think the guild hall could have more stuff to make guilds even more enjoyable than they are right now. Since as they are, it's pretty much a glorified "friends" list. There's no real benefit or anything at the moment. And all of this would be within the guild hall itself so more actually people use it.
First, the guild hall could use a "message" board where member could post whatever they needed the guild to know. Need a certain recipe? post it in message board. In need of guildmates up for jelly runs? post in the message board. Organizing a special event for the whole guild? post it in the message board. A new member needs something crafted? post it in the message board.
Like this, you wouldn't need to spam your guild chat everytime some one logs in.
I know the next suggestion has already been made but I'm going to take it a step farther. Allow for equipping of sword/shield inside guild hall. Having to "inspect" everyone to see what they're using is just inconvenient. Sure this would suck if everyone in haven was running around slashing imaginary fiends, but in the guild hall we want to see the weapons.
And here is the extra step: allow for sharing of weapons! Basically make it into our own personal "advance training" hall and allow guild member to try out different weapons from other members. Sure you wouldn't have unbind or really "equip" the weapon at all, but it would just be temporarily lent to others. It really sucks build up that 5* sword only to find out the charge attack is useless to you.
I agree with the message board idea. The sharing of weapons would work if there was a sort of "Guild Arsenal." If you donate an unbound (keyword unbound) weapon to the guild, then all guild members could use it, and since you donated it you would have first pick of your weapons. Maybe also an advanced training hall as well.