Here is the idea in short note:
A)Guild Treasury
->Guild treasury added in every guild.
->Guild leader manages Guild treasury (perhaps ranks with Configure Guild Ranks permission too)
->Manage allows only to send gold coins from treasure towards any player the officer wishes.
->No one is able to donate gold coins to treasury
->The only way the guild treasure will earn gold will be from this passive tax (we can add more ways latter, like plunder % etc).
B)Passive Taxing
->The guild treasury will earn some gold coins whenever a guild member spends gold that goes back to Avonmora.
->Let's say 0.1%
->So for example, when Roileon spends 1million gold to buy Officers, 10k will go to his [Fox] Guild Treasury instead of vanishing. (so in short, he pays 990k for the officers and 10k are donated to the guild treasury but as he is the leader, this is an effective 0.1% discount for him as he will be able to get them back - this is why the passive taxing will need to be kept low).
The 0.1% is not thoroughly checked yet, just a first idea.
Let us know of your thoughts.