Janome 6600P I have used a decorative stitch for quilting on a baby quilt. I used variagated thread. It was really cute. This was a simple ABC panel that needed help. Fabric was too flimsy to cut it up and border each block so I just stitched through all the sashing with the deco stitch. I adjusted it large as possible. I did get a variable on the size as I pulled, pushed or whatever the quilt through. I could stretch the stitches some that way. Also, used the deco stitch to finish the binding.
Could I quilt a queen size this way? Probably not. There is a tiny stipple deco stitch that could be used within a block. Others could be done in this manner.
Note: for me deco stitches are slow and take lots of thread.