Speaking as the co-author AWS's Rust Lambda Runtime: there's no fundamental impediment for us supporting Rocket (or any other web framework), but I suspect there'd need to be changes made in Rocket to support how Lambda expects input. Namely, Lambda functions don't see raw HTTP requests, but instead, fully parsed JSON. This blog post shows how Lambda expects data to be formatted: https://aws.amazon.com/blogs/networking-and-content-delivery...
I wasn't sure if bare-bones Rust+Lamba-Rust-Runtime was already enough.