I don't see the two as mutually exclusive. The lean startup methodology doesn't care at all what people think about the feasibility of something. What matters in that methodology, however, is whether people will pay for something, if implemented.
A side note is that people telling you they will or won't pay for something can be quite misleading. The act of talking is quite disconnected from the act of actually paying you.
A side note is that people telling you they will or won't pay for something can be quite misleading. The act of talking is quite disconnected from the act of actually paying you.