Just a simple 20% gold refund for contributing to the guild you once belong to. At some point, when someone is kicked, or leaves willingly, or dissolves it as guildmaster to join another guild, it would be nice to not only take your trophies with you into the new guild but also some gold to contribute for your new guild.
Versions 2.1 and 2.2 are primarily focused on guilds, so even the trophy keeping may have exploits soon. There is also the problem that there are many people who have been in several guilds, of which the game has likely not been tracking the total across them all.
I don’t think they should implement a refund. Guilds are a risk for everyone involved. When you join a guild, you risk not liking the people or how it’s organized. The guild owner risks new people being leeches. So, sometimes leeches will get free items, and sometimes a player will donate to a bad guild. Just the nature of the beast.