So I was a bit disappointed with the guild hall update way back when. Not overwhelmingly so, but just a little, because what I was really hoping for was a more interactive experience and what I got was a crown sink and the ability to purchase furniture which is alright but left room for improvement. If there is ever a plan in the far far future to revisit the guild halls and possibly improve upon them, here are some ideas for cool and interactive features that would almost certainly not disappoint.
Monster containment + study
The idea is that you can now capture live monsters in the clockworks and study them in the guild hall! The laziest way to implement "captures" would be to provide missions only accessible from the capture station that ended with a cutscene of the monster being captured with a net or something. The less lazy way would be to actually have the knights go out into the arcade and capture the monster using some sort of device.
Once a monster is captured, it is placed in a cage (an area that is sectioned off in a room) with a mist wall in front of it. An interface (possibly the same one that let you capture it) would allow you to feed the monster excess materials from the guild storage or your inventory in bulk. Eventually, the tame monster would be free to roam your guild hall as a furnishing, or made to sit still/look about if it is a turret/trojan. Guilds that failed to feed the monster in captivity would end up losing the monster.
Another possible reward for doing this could be enhanced damage vs monster UVs against that monster family. Specifically, a ticket that when brought to punch would allow you to get an extra damage vs monster UV on whatever. I don't think this would be OP in guilds favor because such a ticket would ONLY help newer players while being inconsequential to old ones, since older players have more gear and better variants and are probably don't care for a construct med bonus.
Gate construction lab
The guild can now, working together, build their own gate! The gate would be constructed level by level selected using minerals, and each area would be assigned guild furnishings based on what levels were put into it. Since these furnishings would come unbound and gates would be relatively expensive to build, these gates would be lucrative for guild members that aren't strictly interested in improving the looks of the guild; i.e. most everyone that isn't the guild master. They would also serve to partially balance out the want to create a primarily arena oriented area, though I'm sure this would be of great interest to guilds.
Non guild members would be allowed to use the gate, but would not receive any furnishings for doing so. There could also (arcade redux wink wink) be an area that allowed for guildless people to build such special gates.
+1 It's worth giving an incentive to the people who never joined a good guild to try and find one. Makes the game much more enjoyable.