I know you joke, but with the existing costs of fab manufacturing I wouldn't expect that using a diamond substrate would take up that much of the cost. New dia

I know you joke, but with the existing costs of fab manufacturing I wouldn't expect that using a diamond substrate would take up that much of the cost. New diamond manufacturing processes include chemical vapor deposition, which would make integrating with fab processes pretty feasible. I'd guess it depends on weighing the performance graphene can offer vs the cost increase over silicon.