Lots of good input here. Here's mine for what it's worth. There are plenty of ILF options out there. Morrison, Tratech, TAC, DAS, Hoyt etc. If you can't find what you want amoung them your aren't looking hard enough. Also, if you go the ILF route you are almost totally removing yourself from the building process. You will be outsourcing the riser and the limbs? Is it really a Zipper then?
Don't get me wrong. I love the current crop of ILF bows. I've owned a DAS and currently shoot a TAC Firefly. I also have a Warf and a Quinn and have owned a Gamemaster and several other Warfs.
If you go that route you will be in good company as they are all excellent bows.
Personally, I think you should develop a deflexed riser that accepts your own limbs. Design the riser so that it is forgiving and comfortable to shoot. Different grip options are a must. (designing the riser so that it could be shot with no grip, just a simple wrap would also be nice.) Design your limbs to fit the riser. Come up with the proper balance of speed and forgiveness as well as shootability and you will have a real winner.
Design it so that the bare bones bow will compete with the Quinn for price and performance. Have options available to allow some customization. Fancy veneers, dips, fancy grips, wood/glass limbs, carbon/foam limbs. All options that can be added by the customer based on his desires and wallet. AMO sight holes, stabilizer bushings and plunger bushing holes should all be included in the standard riser.Just make sure the shelf is contoured for shooting off the shelf.
You could build some adjustability into the limbs if you wanted to to allow folks to have a bit of weight and tiller adjustment but I don't think is an essential option.
Make it a metal riser Zipper, not a generic plug and play. Just make it affordable.