Only thing perhaps was if this GB gave goods either to the clan pool or player storage for a chosen era, set either in clan HQ or players HQ. But then it might be a very inbalanced GB when levelled high.
First, we have already three (3) GBs that give goods to the guild Observatory, Atomium, and Arc. Most guilds I have been member of, have Observatory leveling up initiatives and seek/motivate each member to work to have an Observatory built. The Arc is surely the most popular GB and players of all eras work to have one. The Atomium is the lest liked GB in this group, probably by its size and its second reward (Happiness) not as impressive than Arc's second reward. With 3 out of 35 (8.5%) I think we got enough Guild's Treasury GBs.
If this GB would produce Guild power points, then the other reward should be something for the GB Owner. Of the main resources that are required by the game (Coins, Supplies, FPs, Goods) there are seven (7) GBs producing Goods and six (6) producing each of the other 3 resources, so I would ask for FPs or Coins instead of Goods. Other option is since we got two (2) GBs providing Supplies Production Boost (Lighthouse of Alexandria and Royal Albert Hall) and only one producing the Coin Production Boost (St. Marks Cathedral) I would suggest a Coin Production Boost as the second reward. Coins are used more than supplies overall all ages of the game, and in higher eras, when the city is pretty much well established, and Coins and Supplies tend to start accumulating there is still higher usage of coins due to the increasing costs of buying FPs.