Before rideshare was conceived of, most regulators would agree that driving people around from point to point on demand for money was just plain old taxi work and subject to the established regulation of that industry. Some regulators still hold to that. Uber came into Pennsylvania, without license from the state or any regulation, and the PUC fined them $12 Million, for the time between them coming in and the establishment of rideshare regulations. The answer here is really the individual states and the legal definitions that already exist in those states. If ride sharing activities meet the legal definition of "taxi" in a state right now BEFORE TNC regs are drawn up- and Uber isn't getting the appropriate license, yes, it is illegal. If TNC activities don't qualify as "taxi" or "limo" or those activities aren't regulated in a state, then it wouldn't be illegal.