I have never started on a DSM, but I have had to unload and change the direction on a quilt I started on my Nolting. It scared the heck out of me, but everything went very well. If you are free motion quilting, and have enough backing, I always have at least 3 to 5 inches on either side and at least 5 inches extra in overall length, I would think there shouldn't be any problems. Since you are moving it anyway, you could add some extra fabric if you need too.
My stitching is different on my Nolting than on my regular sewing machine, so if you are using a thread that will show up, you might consider that a problem. Personally, I wouldn't worry about it unless it is a super special quilt. Think Judy Neimeyer or Jacqueline de Jonge. Some long arms are much better at producing a stitch similar to a DSM...my older Nolting...born in 1997, and my not keeping my moving speed consistent, does produce a variance for me. I just don't sweat the small stuff, and that is small stuff to me.
Edited to add: Worse case scenario...you don't like what you see with the long arm (which I doubt will be the case) and have to do the frog stitch.
Last edited by Barb in Louisiana; 11-22-2017 at 06:51 AM.