Pardon if this has already been mentioned --
Griffitsin, a lectin derived from red algae, has broad anti-viral effects against many viruses (including at least some Corona viruses - as a web search will reveal), but is not currently being tested on the infected, as far as I know. Unfortunately, it does not appear to be significantly absorbed orally. Perhaps, there are agents that increase its absorption, or the injection route may have been tested, or is under consideration?