First of all, the 20 character limit is good but honestly it's irritating me greatly because i'm missing one letter from my guild name.
I feel like a 25 character limit would be better, allowing more creativity without allowing stupidly long names.

Similarly, the ability to change a guild's name for, say, 30 energy, would be good. Perhaps either Guild Masters or the Founder only can change it. Having the extra S on my guild's name would make me happy, to say the least, but I don't really want to disband and recreate it completely - assuming the above change does ever happen - just to add one character, but I don't want people infinitely changing a guild name just to irritate people.

Speaking of guild naming, though, the ability to put custom names on guild ranks (Padawan, Jedi Knight, Jedi Master, etc for a star-wars related group, for example) as well as the ability to implement custom ranks (that ultimately move into the 3 existing rank types - member, officer and guild master)