Cool deal 'rat, I totally get where you are coming from, and I agree about ILF- its really neat and fun to mess with but for me it just makes me obsess about the tuning and I figure why bother if I have a bolt down bow that works perfectly for me. I will say some folks just crank down a lighter set of limbs to the max and basically make it a bolt down if its a particular setup they like.
I guess what I was getting at is that to me its about design constraints. Some bowyers have the time and means to develop something that fills the niche...Gregg Coffey is currently perfecting a 60" Elkheart for example! It may well prove to be his most brilliant creation yet. And by 60" Elkheart I mean a bow that has the same riser length as a 56 or 58, but just with longer limbs. He tells me it will go to 33" and guess what the draw force curve for it I got to see proved it. So that is a successful development of what started as a short design being made longer. 60" isn't long as you're wanting, but its a big step for a bow (Elkheart) that is typically ordered/offered in 56". The best part is the 60" will still shoot beautifully at even 27 or 28". Gregg's done good and I know if I add a second Elkheart to the stable someday I will try the 60" as a supplement to my handy 56er.
Other bowyers just may not have as easy of a time extrapolating a longer version from a proven short bow design. It may open a whole new can of worms, or worse yet reduce or eliminate the best qualities of said short bow. You follow? Like for example, if you make the limbs longer you also might have to make them lighter to give the same energy return for a given draw length...how do you go about shaving the weight? Oly limbs are carbon/ composite construction for a reason. You have to have quick recovering limbs on a 70" bow drawing 28-29" or its gonna be a dog. Just physics. It'll be smooth as butter, but the 64 or 66" bow of similar design will be snappier as along as your still within its smooth range and not stacking. Or something to that effect, I'm not a bowyer so I think I'll leave it at that.