Deno is a next gen runtime for JavaScript (and TypeScript) ideal for scripting and serverless. It has little overhead, and imports modules directly by url (stores them in a local cache) meaning that no node_modules folder is needed, not a vendor bundle.
The initial support for Deno functions could be to provide the runtime and share the module/dependency cache between the runs.
For DO to save in bandwidth further on, would be to cache public external urls globally for Deno Functions, and private (behind auth) urls only for the function itself. Another thing to consider would be the initial caching of the ts->js transpilation, but this could be a one time deno cache call.