Yep, I think that the prospect of trying to achieve real cell phone like qualities out of mesh networks is a no hoper. The real question however is what the end consumer will accept. Often times products are over-engineered / overpriced (whether deliberately or accidentally) beyond what consumers really demand and it's not until a low quality competitor shows up that everyone realizes it. Think how the vast majority of consumers turned out to be happy with low bit rate mp3s after recording studios spent years pushing CDs, and how very few people really care about HD vs SD very much (at least, not on smaller screens). So perhaps there's room for a network that just doesn't work while travelling at 75mph (or even 30mph). So what? Maybe consumers just don't care that much if they are getting it for free.
The 75mph isn't really the hardest part of that. Really, it's indoor coverage with dirt cheap consumer gear that's hard, followed closely by call and data connection handoff. Even if it's free, there's a minimum amount of service quality to even be considered useful, and I think handoff and indoor coverage are both essential for mobile wireless to work. In modern networks, handoff is also deeply tied to availability in high density areas.
