Great Idea!!!!
The leaves will look so much better if outlined quilted, than using an allover quilting design.
I do see a couple of potential hitches ... but not insurmountable!!
* With the quilting already done, would the Steam-A-Seam "fight" with it? Meaning, the flatness that the SAS wants vs. the poof that the quilting would have; then wanting the leaves smooth and even stitched in place.
* Are you content with the blanket stitch showing on the back, with the lines running through?
I'm thinking you have already accepted the backside quilting effect. For the SAS challenge, I'd make a placemat, runner or WHY, to check the technique before making the "real" quilt! Maybe I am overthinking this, but I'd sooner check it out than to say later, "Now what am I going to do?"
Look forward to seeing what develops with this one!