I think the issue of tax is actually potentially good for bitcoin, now hear me out. It may be that they won't even attempt to make it illegal because they won't want to try to make it illegal, admit they failed(like the way of the torrent), then try to tax, so they may just skip right over trying to make it illegal and go straight for the tax, which, granted would be tough for them to enforce considering the nature of the project. Many people would most likely willingly pay taxes on their profits though, at least somewhat, so that they can spend there money openly on things like houses and cars, anything that will easily be noticed by them.