It's definitely bad news in yes of the ease of buying bitcoins but it could help it seem more trustworthy in some naive people's eyes. I don't think it will affect the price either way, although it may affect the adoption rate in Japan.
Something legal would be a lot more attractive than something that is uncertain or does not yet have legal proof. So if indeed Japan Trust bitcoin as payment, it will be more and more people are using bitcoin in bitcoin. And you need to know if more and more users bitcoin then will be higher prices, because indeed the level of demand will be much greater than the availability stock in trade.