How about taking what's good about BOSH and carrying that forward into something better? What could be added to Terraform or PaaSTA or something to make it as good as BOSH?

Terraform's model (local state files) is not something that works well, in my opinion. Since AWS doesn't know that you want some operations done "transactionally" (like with CloudFormation), you can easily end up with a half built env that needs to be cleaned up. PaaSTa is more of a CF competitor, as far as I know, not really at the same abstraction level. I think that it would be a lot easier to clean up the UX/marketing of BOSH than doing the opposite.

Have you looked at bosh.io? It's being actively worked on by our designers and engineers, I bet that feedback would be welcome. If you email me I can put you in touch with them.