I prefer to ask another question: "Is this useful". Would it be useful, if we were to spin up a different platform in the future, to be able to do so without LLVM. I think the answer to that is a resounding yes.
That doesn't leave rust stranded. A _useful_ path for rust to pursue would be to defined a minimal subset of the compiler that you'd need to implement to compile all valid programs. The type checker, borrow checker, unused variable tracker, and all other safety features should be optional extensions to a core of a minimal portable compiler. This way, the rust compiler could feasibly be as simple as the simplest C compiler while still supporting all the complicated validation on platforms with deep support.