I'm also one of the many that would like to see some info on these Big Battles and maybe even some info about a new cluster and raid being in development, before I decide whether to purchase the expansion or not. I enjoy leveling characters and should have 9 85's ready for HD, but without something substantial to do at cap then I just can't be bothered.
To briefly touch on raiders leaving en masse, each person will probably have a different story to tell because I'm sure on some servers they have left, on others they haven't. I know from my personal experience that my kin is practically dead at this point. We were a top raiding kin back in the day of Rift and Hele, stayed that way with moria with DN, then started to taper off once BG came out. There wasn't enough content coming out to keep people interested and we went from having 2-3 raid groups down to barely being able to get enough for 1. At this point the majority of the people I've been raiding with for the past 4-5 years are gone and the kin is a ghost town. Personally I used to be one of those people there raiding 3 nights a week on a handful of toons and it was enjoyable content and everybody had fun. Now I, along with a large number of our raid, have either quit or only log in sporadically.
It's just disappointing because so many of us are huge fans of some of the raids that have been designed in the game (Rift will forever be my favourite group instance) and over the past few years it has been in steady decline. Maybe it's a cause of the player base not being there to meet the financial costs of that sort of development, maybe some of the developers have moved on to other Turbine projects or maybe it's simply a shift in focus to the simpler more mainstream things in the game. Regardless I along with many others had some great times raiding in lotro and hopefully someday we get something similar to it again.
So yes to more info on Big Battles and raids in general hehe