This issue comes up once every month or two and the comments are always the same, so allow me to summarise the main points for you, and save us all some time.
The main argument comes from a very small group of players who don't like people outside their fellowship donating to their wonders, because they would prefer the prizes only went to people in their fellowship, and therefore propose a game mechanic that will allow them to restrict wonder donations in some way as a solution to this issue.
The response from the devs is that they will not be changing things, as this is how the wonder donation system is intended to work.
The response from the majority of the player base is that if you don't want people outside your fellowship winning the chests then you just have to make sure your fellows donate enough KP to your wonders that it is unprofitable for anyone else to consider it, or if they try, they at least don't manage to get the main prizes. A simple but effective way to achieve this is to use KP exchange threads. Essentially, you already have a simple and easy mechanism to achieve what you want to achieve, with the benefit that it won't negatively affect anyone who doesn't have the same play style as you.
Most outsiders who donate to your wonders only drop a handful of KP in, so it's not hard to bump them out. And for the rare occasion when someone drops such a huge amount of KP into your wonder that your fellows can't get one of the chests, does it really matter? The outsider has significantly reduced the amount of resources you need to upgrade your wonder, so you are receiving a big benefit from this practice regardless of who gets the chests. Anyone who's giving you such a big gift kinda deserves the prize at that point.
I think that's all the key points. Have I forgotten anything?
