Honestly even though i make fiberglass jetpacks, i think this is definitely something you should keep at. Once you get everything dialed in, the option of being able to make ANY size is a great thing.. Not sure if you can get it much lighter than a fiberglass pack without going a little thin on the plastic and making it a little weaker, but you can def get it lighter than the resin packs. This is a good idea, i think you should run with it. Just keep in mind what it may cost someone if you were to sell them and if its worth your time to do them compared to the costs.
I also love the little test pack haha!