I highly doubt that the government of Japan will allow the boxing match in Tokyo. As per
https://covid19japan.com/, Tokyo has the highest cases of Covid-19, so it's not likely that they will simply go there as venue alternative.
Besides, I also don't think that Arum will allow that fight to happen in Japan, we all know how Arum works, its all about how big Top Rank can milk this fight. I guess it is Inoue statement alone and not representing Top Rank, perhaps he just blurted it out of frustration because he is eager to go fight the best version of Casimero at this point.
Aside from that, the entire Japan is being put under a state of emergency. This is in place until May 6. In line with this, the government is urging people to remain in their homes. So I guess this match will be put off indefinitely pending the stability of the situation. After all, both Japan and the US are suffering from the blow dealt by COVID-19.
Looks like you guys got mislead. Inoue's thought of relocation is obviously will not take place while the whole world is currently dealing with the pandemic virus.
Of course, it should be after and not today. Since Vegas got hit by damage, the fight might not take place there immediately once the virus is manageable. So for an alternative, Inoue thought it might be better in Japan.
Although I agree that Top Rank will always consider a bigger market but I'm sure they are considering relocating for the fight to push through. Maybe on the other US States that not got heavily affected. These people are business experts and looking at all sides before executing. Again, not today.