In general, Japan had a good run with the legality of BTC, of course they are worried that the price might influence the economic activity, so they're trying to be a bit careful about the legal framework. Considering however that Japan has been fairly open to crypto innovations (XRP included), I wouldn't worry all too much, as it's a tech savvy government and population which can more easily identify the potential of the blockchain and how it can help people. Besides that, even if things get out of hand, you can still send the BTC outside Japan and cash in from another country, if your stack is big enough it will be cerntainly worth it, otherwise just give Japan some time and they'll sort things out (integrating it in their legal framework).
I definitely don't think Japan will outright ban cryptocurrencies as I agree with you on how savvy they are on technology. They might regulate ICOs, which could be considered a good or bad depending on the regulation.
What do you guys think would be a good regulation, lets say from a country like Japan or US?