I can't think of any reason for not doing it. It would be very interesting for sure. I have thought about doing it several times but just haven't quite gotten it done. I have learned to do starts and stops that are not obvious on either the front or back. If you use the same color thread on the top and bottom it should not create a problem. Be sure to let us know how it goes.

I've done it and is works out fine. Once though, I changed my mind about how I wanted to quilt it AFTER I had pin-basted on the front and had to re-baste it on the back. I suppose that would be a plus for spray basting......you could more easily change your mind.

I've done both ways. If I'm using a matching thread on black or near black, I'll often fmq with the back up, since that is usually a print fabric and I can see where I'm going easier. Try it both ways and do whatever works best for you. Try out some sample sandwiches and see. If you can make your sandwiches out of the same fabrics as your quilt, you'll be able to see what it'll look like on your quilt.

Sometimes it is hard to trace the design with a stencil, dark and lights in the print. I just tried exactly what you are asking a few days ago. It worked fine, but I think some designs will come out with the design reversed. (not sure)