I bootstrapped a QnX compatible kernel (with GNU userland) in about 2 years that was then used to power a bunch of special purpose routers. Yes, that's the easy part. As Jacques_Chester already remarked elsewhere in this thread the community part (herding cats) and getting the required buy-in is the hard part.
The first can be done, I'm 100% sure of that, the second I'm not so sure.
I'm kind of surprised that on HN of all places something like a kernel would be considered somehow beyond re-creation or requiring special god-like powers.
It requires a good work ethic and a lot of time. It also really helps if you are an experienced programmer. It definitely is not easy but that's more to do with how you organize things than with the actual complexity of the code and a microkernel is super helpful with this aspect, it is far easier to hit the right structure than with a macrokernel, you're more or less forced into doing it right without any way to give in to the temptation of taking a sneak peak at a data structure that isn't yours.
The first can be done, I'm 100% sure of that, the second I'm not so sure.
I'm kind of surprised that on HN of all places something like a kernel would be considered somehow beyond re-creation or requiring special god-like powers.