We have the exact same issue ! We are always at 500 and have to constantly cut inactives to recruit. We stopped actively looking but people's friends and whatnot always want in so we have to cut.
We tried the chat channel thing as well between 2 guilds .. for some reason as you said people just didn't use it the same as guild chat, and ya when looking for a fill in for an OP, the people in the "other" guild rarely got picked.
BW wanted us to ban together yet limits us from doing so. They even dropped like 100 servers or whatever.. I totally don't get the limit on the 500 members. Back in the day in WoW some guilds were over 5000 members...
Could we get a word on this please!!??!!