Social improvements
The tricky bit is the Guildy bit.
In order to discuss it fairly, I think we have to define what it is: an association of like-minded people who collaborate.
Some will collaborate with a view to being hostile to other players, but that isn't an issue with Guilds per-se; but a shortfall in the crime/punishment systems in the game and I believe that's where it should be addressed. To explicitly say it - a guild is not above the law and should not be permitted to act with impunity. It's up to FD to sort that out (and it's a problem in the game already, excluding the random abandonment of law which is PowerPlay).
Basic functionality a guild needs within the game is basic, really just delegation of authority from the creator of the guild, grouping controls and chat. Essentially an advanced friends list.
We want the guild to be non-intrusive. There are good suggestions earlier in the thread, so I'll just say it can be done and can be transparent to players who don't really give a monkey's about it.
Guilds own nothing. No shared ownership of any sort. Perhaps money transfers would be permitted within the guild - but that's it.
However, there are groups of players who fancy guild vs. guild actions - so within the existing engine perhaps the guild could be flagged IF THEY HAVE COLLECTIVELY CHOSEN TO BE A COMBAT GUILD (so it would be an attribute of the Guild, set by the owner and clear to people who might consider joining them). Again though, the law applies within populated systems.
How does that sound?