My sister and I share a serger and the machine has 1-4 thread capability. I can't see why you couldn't FMQ using 1 thread, but it probably has something to do with the sideways and back motion of FMQ which is a no-no on a serger.
I recently saw a YouTube link on a serger quilt that was really cleverly done, pretty much QAYG.
Has anyone made anything larger than lap size on a serger? Since the throat isn't that large, I'm curious how much harder it might be to do a larger quilt.