You do know about Muse headband, right? They did exactly this and it works great. The company seems great, solvent, they have just released a new version of the

You do know about Muse headband, right? They did exactly this and it works great. The company seems great, solvent, they have just released a new version of the hardware (including an HRV sensor), and it actually works. Not sure why your kickstarter failed, but Muse headband is exactly what you are describing, it's a finished polished product and it actually works (speaking from experience).