I am NOT the Quilt Police. I think everyone should do what floats their boat. However... I have an experienced friend who mixed batiks and regular cotton quilting fabric in a quilt once, and she did struggle a bit. She said the quilting cotton had a lot more give to it, while the batiks didn't, and seams where the two met were somewhat challenging. She said she wouldn't mix fabrics again. She used a package of Bali Pop batiks. Her quilt turned out beautiful, though! Here's a picture:
http://www.seamstobeyouandme.com/wor...1/06/Nancy.jpg