It is definitely a protein and I don't see much use for mRNA here. Clearly, there's nothing about the produced protein that marks it as safe just because it was

It is definitely a protein and I don't see much use for mRNA here. Clearly, there's nothing about the produced protein that marks it as safe just because it was produced in the body's own cells, otherwise the vaccine wouldn't generate a response. So all this would do is introduce a lot of protein directly into serum. If someone was allergic, that would cause a reaction, and if not, it's not clear what it would do. It may not be a good idea for it to suddenly appear in the body without having been exposed through the GI tract.