Any new business can establish an equivalent to uberpool once they have critical mass. Since many markets are small the relatively cost of establishing this mass is not excessive.
Yes network effects are real - the question is there much of a network effect with the taxi industry. History suggests there isn’t, but the current valuation of Uber suggests that a lot of smart money thinks there is such an effect.
Actually there is a lot of history for this - go to any third world country and this is how most of the taxis for locals run. It is actually one of the outcomes of a lack of enforced regulation since competition drives unregulated drivers down this path.
