I read through the LOTRO dev chat log posted on MMeOw (also on the official site), plus Tony's followup notes.

Some highlights for me:

• Pet Pathing fixes - Yay, I'm pleased to see Turbine is working on this. As a new player, I have no idea how long it's been a problem, but I've gone through the same thing with pet classes over and over through multiple MMORPGs. Hopefully this means mob pathing will improve as well.
• 3man Instances - This is the feature from the expansion that caught my eye in the first place and got me trying the game. I haven't actually reached those 3man instances yet, but I'd love to see them make as many as possible. Glad to hear they're popular.
• Raiding - I'm glad with the raiding that they have, they're currently concentrating on 12man. I'm really not interested in larger raids anymore, I don't feel that the content improves by throwing more players at it. 12 is plenty.
• No Housing changes - I'd like to see housing improve. It's pretty good, but it doesn't have the same high attention to detail as the rest of the game. A shame it's not much of a priority. An address book for neighbourhood locations is a good idea though, I hope they implement that suggestion.
• Fellowship Maneuvers - I'm not super fond of the 'Conjunction' system, mostly because it doesn't flow with the combat, it's more of an interruption. It must be a nightmare for their designers to balance encounters around. So less emphasis on it is actually something I welcome.

I hope they have an ETA for this soon. I was really hoping we'd get a release date. It's the first Book patch for me, so what can I say, I'm curious and eager to see it.