Many of us have multiple linkshells. I, for one, find myself sticking with one or another for extended periods of time and losing track of friends on the others. While the portability between linkshells is vastly superior (in my eyes) to the guild mechanic (you're stuck in one guild at a time), it still retains that "one at a time" mechanic that can be detrimental to keeping in touch with all of your friends.
What I would like to see is an interface that allows you to equip multiple shells at the same time. Imagine being able to have your HNM shell, your dynamis shell, your assault shell, and a couple social shells on all at the same time. An equivalent to your keybind for opening your chatlog or removing buffs could first scroll an interface showing your first 4-6 equipped shells letting you choose which one is your active shell for /l chat. This would prevent furious shell changing to stay informed and would further tie the community together. Further, it would allow people to remain in their social shells and still do event activities without forsaking their friends.
I personally participate in a pet shell, a social shell, and a dynamis shell. Having to shut out two groups of friends so I can be with this third has always grated on me. Further, anyone that has played as a member of a social shell knows how often people eventually gravitate out of the shell for bigger and better things and it eventually destroys these small communities.
Imagine having an interface next to your chat window with five pearl icons lined up vertically and a box around one of them (set as primary). /l chat would go to that, or you could quickchat to any using /l1-/l5. At the beginning of any /l chat line in the chatbox would be a pearl icon (or three letter LS name abbreviation) to identify which linkshell the person is in. An interface like this would dramatically increase the viability of the linkshell system and would be a massive boost to community building in the game.
Of all the newfangled things they're going to do in FFXIV, this is the one thing I hope gets done more than any other.