Although for different reasons, I think this would be a great idea too.
I use linkshells a lot, as for example friends who are in different fc's are there. Old friends who have quit but log in once in a while are there, as are people from fc's I used to be in.
I have always generally gone solo in these types of games, (in fact ffxiv is my fist mmo being in a guild-like organisation), although still talked to people I have befriended.
I do like fc's don't get me wrong - you meet a lot of different people, both which you do or don't get along with, and this can be interesting. I also like having a room, and spontaneously doing duty's you wouldn't do on your own is fun. But having to be in an fc to know who's logged in/out is somewhat limiting.
It doesn't have to be something big, just a button to click so you can see if someone logs in or out in that specific ls. Something similar to the notification settings on chat groups would work perfectly.