Thank you Prism (yet again) for the wonderful advice. I like your explanations on many points. You are a great resource! I think after reading all of this I am going to get some muslin. I definitely do not want to use an interface that could disintegrate over time as you guys have mentioned. Defeats the purpose. I was also worried about the permanence of the placement of interfacing. With the stretchy quality of the quilt, one little wrinkle or stretch while ironing would be a disaster!
I will also look into the threads you've mentioned.
One more question: When I requilt it, I was considering switching to free-motion, in a modified stippling pattern, rather than straight-line. Do you think free-motion or zig-zagged straight line would be less likely to pop? I think the linear nature of my original quilting makes the thread more vulnerable if it were to get pulled. Makes sense in my brain that switching direction, as you do with free motion, would help, but I'm really not sure. I do like the pattern I went with originally, so maybe I should make another test sandwich with the muslin and zig-zagged straight line to start with and test how it holds up. Hopefully the stability the muslin provides will be enough that I don't need to worry so much about the quilting pattern itself. After all, if I eliminate the stretching, I eliminate the problem essentially, and it should not be any more vulnerable than any of my other quilts.. in theory!