I had an idea for a new guild feature that I think players would love, that could be implemented using existing game mechanics to avoid reinventing the wheel.
Currently, there is no good way to experiment with arena team builds without risking losing rank. You can try a new team build live in the arena, but if it is bad you can set yourself back for days worth of fighting to reattain your rank.
Also, within guilds, people often talk with guildmates about new team builds, but there is no way to test anything. You can talk about what MIGHT be an effective team, but guildmates are frequently in different shards and there is no way to test the builds amongst friends or try anything out.
I think it would be great to add a training area to the guild screen with two modes:
1 - Guild Dojo - This would function just like the arena for guildmates, but would have no rewards and unlimited plays. Basically, just a place for guildmates to set a lineup and let everyone else to try to beat it and give feedback. This would be a great way to test strategies without blowing your points or rank for the day.
2 - King of the Hill - Similar to #1, bit there is one player (the leader/king) that sets their team and everyone else tries to beat it. The system could allow each player to wager a set, minor amount of their personal guild coins (maybe 25 or 50) each try. To play, you place your wager and attack the current leader/king. If you win, you double your coins (from the leader's stash) and take the leader's place as the king (until beaten by someone else). If you lose, the leader keeps the coins. This wouldnt unbalance the game because it doesnt create any new currency, it just lets guildmates battle for bragging rights...like a friendly poker game. If you keep the bet amount low and level (ie no raises or increases in bet) it also wouldnt penalize players much for playing. Just a little something to make the contest mean something.
I think these two modes would be a great addition to let players experiment with builds, interact with guildmates, and pass the time when they run out of energy for the day.