It seems like the title may be misleading:
"We propose that the immunomodulatory effect of hydroxychloroquine also may be useful in controlling the cytokine storm that occurs late-phase in critically ill SARS-CoV-2 infected patients."
This seems like:
a. This would have no prophylactic benefit (to avoid infection or reduce early symptoms)
b. The benefit would only apply to people who are already in the late stages and experiencing a cytokine storm
As hydroxycholoquine is immunosuppressant, I might suspect that its use in non-critical cases could actually worsen outcomes by suppressing the functioning immune response. As someone who was looking into it as a potential tool in the prep kit, I think this is likely a drug that is best administered only at the discretion of a doctor.
Would love to hear opinions from others who are more knowledgable though.