The current guild leveling mechanism with renown decay makes DDO into a very unfriendly place for casual/social players and encourages abuse of new players by greedy guild leaders. So here is my proposal for fixing the problems permanently:
1. Remove renown decay.
2. Make guild levels (practically) unlimited. Perhaps have a hard cap at level 4,000,000.
3. Make level 101 require the same additional renown that it takes to go from 99 to 100 now plus 1%. All levels after 101 would require the same additional renown as the previous level required plus 1%.
4. For every 100 levels a guild attains after level 100, they get an in-game announcement and a 1% discount on all airship ammenities rental contracts - capped at 60%.
5. Any guild that kicks out or forces out more than 60% of their total members over a period shorter than 6 months and does not replace them with new members in another 6 month period, goes back to level 25. Members leaving voluntarily on good terms do not count for this but members leaving on bad terms do count.
6. Leave everything else about guild leveling as it is now.
Item #5 is to prevent abuse of new players by a greedy guild leader. It would prevent such a guild leader from inviting a ton of new players to his guild to level it up and then kicking all of them later so he is left with a higher level guild all to himself and maybe a few of his friends.
Under this plan, ALL guilds would be able to advance (practically) indefinitely. No guilds would be forever stuck in place. Most guilds would not try to shoot for the crazy high level cap so there would be no incentive to kick out casual and social players. DDO would be a more casual and social player friendly place. Guilds that are stable and have been around a long time will be able to achieve high levels regardless of whether or not they have lots of casual players in their ranks. In fact, guild stability becomes an advantage in this scenario and guilds that are not stable will never achieve high levels.