After a lot of thinking I finally decided to focus on studying the fusion of bluegrass and other musical styles.  More specifically I'd like to interview people and ask them about their choices when playing songs.  For example at the last jam I went to I noticed that two mandolin players had rather distinct styles.  One player played a very traditional bluegrass style of mandolin, very much in the style of bluegrass mandolin players out of the 1940s and 50s, while the other played a style that was often associated with some early jazz mandolin and cross picking style, the jazz style very much like that of Jethro Burns (Here is a clip of Jethro and Chet Atkins music starts at 1:48 http://www.youtube.com/watch?v=9wGUPN9-cj0 )  and Jesse Mcreynolds who was known for using cross picking on the mandolin (Here is a brief clip from an instructional video he did on cross picking for those who don't know what it is http://www.youtube.com/watch?v=aiyF52PiDz4 ).  Both of the mandolin players at the jam were obviously respected, but I've always been curious why popular bands usually play a more progressive bluegrass style, borrowing from current and popular musics a lot more than the average bluegrass musician.  While it might be a a difference between performance and jam styles I would like to explore this further, I don't have any particular literature to look into, but I'd like to talk to the people in the bluegrass community and see how people feel about the incorporation of other musical styles and why they do or don't incorporate other musics into their playing style.