Wow, many of the complaints against increasing # of membership seem from players too lazy to recruit or wanting to deal with the hassle of managing a larger guild. If you look at the environment now, successful guilds have gone around the problem of membership limitation by starting up sister guilds. I think it is much more of a hassle trying to run 2 or 3 guilds then it is to run a single guild. Increasing the # of members would allow GMs to not have to turn away as many potential recruits as our current 30 member limit.
For those GMs who are complaining of going through the trouble of recruiting and/or managing a larger guild, there is something called delegation. Use the resources at your disposal.
I, for one, would love to see the limit on membership increase. It would definately help guilds deal with the increase in tasks 4.7 would bring.