1.Guild alliancing
Well, there should be a 'guild allince' where you can't kill the guild members of your allianced guild in gvg and can boost each other guild members. The guild leader can send an alliance requet to other guild and they can accept or decline the request.
2.Boosting %
When boosting your guild members, there should be an option to set '%' if xo that other guildmate gets. This can prevent xp-leeching, and make boosting more faster.
3.Co-leader
There should be a co-leader.One leader is not enough if you're running a huge guild.