It doesn't matter how great your tanks are, hydrazine will never be suitable for commercial passenger flights. It's insanely toxic and hazardous to deal with. Forget the passengers, that stuff is dangerous for everybody on the ground too. It's not cheap either, I'm not sure why you'd think cheap sub-orbital flights are gated by hydrazine tanks.

Also, old intercontinental supersonic flights aren't done anymore, the Concorde is gone and nothing replaced it. It will likely never be an economically viable niche, particularly since the utility of video streaming has been so conclusively demonstrated, soaking up much of the demand for business travel.