I'm not 100% sure the reasons for capping guild sizes at 24 players. I'm assuming it's just to limit the speed at which you can grind out commendations (if there's more to it than that, this idea might not work).
My idea is to keep everything as it currently is up to a guild size of 24, but rather than capping the guild at 24 players, you can have as many as you want (or at least a much higher limit), but rewards scale negatively with guild size (i.e. the more players you have, the less guild rep you get for each accomplishment).
As long as it was balanced properly, a guild with 100 players wouldn't be able to achieve commendations any faster than a guild with 24 (and might even be slower) because reputation gain would be scaled down accordingly.
My reason for wanting this is that I (and I'm guessing I'm not the only one) don't join guilds for the reputation and rewards. I join to find a friendly group of people to sail with. I like the mechanic of logging in, seeing that someone I like sailing with is already in a sloop, and just jumping in with them. It's a great system that I think could be expanded and made more flexible, without needing to tie it to in game rewards and commendations.
Alternatively, keep guilds as they are, and introduce a new system ("Fleets" maybe?) with no (or much higher) player caps, but remove rewards entirely, so it's just there to facilitate sailing with friends.
