The only real features I see as plausible that's been suggested is guild houses actually being what they are, in terms of a place members can drop furniture into one place (not the leaders GH, an actual guild house that links to the guild).

A log to see the recent activeness of members, you'd have to be given the power to access it.

Something about joining and leaving, I can't remember what exactly was suggested, but it was a good idea.

Things such as 'a daily guild boss quest' seem silly on Classic standards, imo. I'm more inclined towards guild vs guild activies/minigames such as CTF, war etc.