I believe Bitcoin is among the sustainable things out there that does not have to work with legal acceptance. As long as it does not cross the illegal border, it should be fine. I think there are a few parameters Bitcoin has to overcome should it seek global acceptance. It might give up some of its unique characteristics in the process, but I do hope that it can still be set apart from fiat.
But Bitcoin has been the same since its inception for most practical intents and purposes, right? So how exactly do you define "as long as it does not cross the illegal border"? As I see it, it is not and will never be Bitcoin's fault if it "crosses" that illegal border. This border is not defined by Bitcoin, whether it is legal or illegal is defined by neither the community not the devs behind Bitcoin. It is defined by people who essentially have nothing to do with Bitcoin other than declaring it "illegal". Which is to say, who is actually crossing the borders here?