Cool idea to use your own kernel though it does sound like you could find yourself in perpetual development hell. And, don't forget all the sufficiently powerful SoCs are super closed. You won't be able to leverage any of their existing driver work and you will need some serious clout to get access to their documentation, with some really scary NDAs attached. However I'm sure you know this and took it into account. Very cool. I hope you will manage to get it to market!