What about a row by row where the theme is picked by the starter of each quilt?
Say you have to start with a row....up to 60" long and then you pass it to the next person. You declare your theme when you sign up. Say I want a black and white themed quilt.
The first row could be 5 sampler blocks. Then the next person decides to to applique, then the next does.... embroidery... or they do another sampler. This make sense? Kinda like the IRRs but in rows instead.