Perhaps I was unclear. Performance is critical. They just shouldn't worry about the kinds of performance issues that can be optimized later. These include thing

Perhaps I was unclear. Performance is critical. They just shouldn't worry about the kinds of performance issues that can be optimized later. These include things like language choice and other micro-optimizations like zero-copy, etc. Getting the abstraction right is making something that can perform well once it's optimized. That is, you worry about the high level performance properties -- things like how it will perform asymptotically -- when figuring out the abstraction. For this project especially, the really difficult part is figuring out what those abstractions look like. Even having to do a complete rewrite later on in a faster language isn't that big of a deal cost-wise.