I initially didn't like the high level idea, but I warmed up to it. My only concern is that the constructor isn't guaranteed to define the same fields with the same types, which kind of defeats the point.

I'd improve this proposal in two ways:

1. Explicitly define the layout with types. It's new syntax already, you can be spicy here.

2. Define a way for structs to be directly read into and out of ArrayBuffers. Fixed layout memory and serialization go hand in hand. Obviously a lot of unanswered questions here but that's the point of the process.

The unsafe block stuff, frankly, seems like it should be part of a separate proposal.