There is only so much speed that is available, given the current "restriction" of 5 gr/lb, a 400 fps bow is not possible. As stated above (I'd love to see how you calculated it, but it matches what I have seen elsewhere), it is against the laws of physics, UNLESS some new technology comes along that actually creates energy during the shot. Even with a 0% letoff bow, which climbs to max poundage very quick and stays there, it MIGHT be doable, but would be unshootable. You would need to get ALL friction out of the system: calbe slide, axles, string against cam grooves etc. It would be 100% dead quiet, no vibration/shock.

things I think you will see:
- I predicted something to quiet them down a couple years ago, poof, parallel limbs have done a good deal of this.
- riser design/construction to make the bow stronger and cheaper to remove any and all bend during the shot.
- Limb materials/design
- cam design to get the speed with a smoother draw curve

I would LOVEto see the price come down, this will take manufacturing technology, not bow technology. Or maybe materials/plastics technology.

We will see advancements in aerodynamics make BH flight easier (heading this way already), new arrow materials, for cheaper more durable arrows without the drawbacks of carbon/aluminum.