I was thinking the other day and it's something iv seen in another game.
It's basicly a clan that lvls up and maybe sts could implement something like that.
But with tiers and every tier gives a benefit
For example:

Like bronze tier - pots cost 10% less
Silver tier - elixers last 5% longer
Gold tier - everyone +5% boss damage
Platinum tier - elixers last 10% longer

Something like that, it's just an example so rewards could be different from above, maybe include a guild banner or a pet/vanity reward.