I've always felt that the guild system is a tad basic and it doesn't make me feel like im actually part of a guild like it does in single player TES games. To fix this I think it might be fun to add guild quests.
I think adding Quests to the fighters guild where I might go kill a group of daedric worshipers or hunt a daedric boss. Something more daily like would be to stop a dark anchor or a daedra incursion.
For the mages guild I thought something to show they are collecting lost lore would be good. Maybe delving in to a ruin to collect a book or relic. or something more magical like exorcising spirits from a home or ruin.
Please post thoughts or comments I would love to see them