Ok, really, there isn't much point to guild halls, so guild masters should be able to modify them a bit.
It could work like a level builder, place a crafting machine there and a billboard there, or mabye an auction house outlet.
Maybe you could pay extra for a larger space, or pay for exclusive npc shops. The guild hall would probably have to be closed while the guild master creates it. Maybe you could have an exclusive guild gate, where members have to put in materials to generate levels. And the billboard mentioned earlier could work as a news blog, with officers and veterans and guild masters posting information and planning runs or something.
Also, it would be awesome if the guild master could make an exclusive-to-the-guild weapon, for the rest of the guild to use, and have a special crafting machine specifically for it(like king krogmo's one in the arcade)
The guild master could choose how many stars it would be, choose a name, choose a weapon to base the weapon look on, and choose aditional effects( shock, fire, surse, etc). All these things would affect what materials are needed to craft the weapon, so if you based the look on a brandish you would need to put in a brandish to craft it.
for example:
name: Astral flourish
look base: flourish
stars: ***(3)
effect: stun
attack type: shadow/piercing
glow/style: purple
charge attack: A lunging double thrust followed by a slash. (same as flourish)
---
crafting fee: 1500crowns
CE fee:200energy
materials:
flourish
dark shard, 10
sharp fang, 3
swordstone, 1
forbidden fruit, 1
phial of phear, 1
So guilds could have their own unique weapons (or maybe a set of them), and these could be non-tradeable to keep them exclusive.
The same as above could go for armours or shields or bombs or guns or trinkets or whatever.
Oh, yeah, so I can make a 10 crowns, 1 energy, 1 swordstone craft for something that's more powerful than a Leviathan Blade? Or am I misreading this?
I think the ability for people in a Guild to pool together any un-learned recipes into a machine that lets anyone in the guild use it would be good - upside being sharing, downside being you have to go to the Guild Hall to use it, but custom recipes are asking for trouble.