How is that different from Node.js which also runs in a single process? Or does Deno create per-request processes (or v8 "isolates" etc) like CGI does?
If it was more along the lines of "I want to use this array helper library, but it shouldn't have any permissions" then it would be a lot more useful, but right now if your Deno app needs any file or network access, then all of your dependencies get access too.
We have so many dependencies that really only need to work in-memory and have zero IO needs. That part is not solved in Deno at all.