Getting straight to the point here, I think it would be neat to stitch spells and pets? I know neither of these can be reasonably expected to happen, but hey, fellas gotta dream.
So pet stitching would be nice. Let's say you got a pet with incredible stats, and a pet that looks real cool. Just put 'em together! It couldn't be called stitching, but, knowing Kingsisle, they can come up with a good name when the time comes.
Next I propose spell stitching. Like for example the animation of Frost Giant on the stats of Snowball Barrage, which heaven knows I would absolutely love to have. I wouldn't even mind if it was just by individual battles! And I understand the limitations of 'single hits need to be stitched with single hits', but I could see this one having a lot of potential, as opposed to the pet stitching one not being implemented due to it being a moral grey area.