Practical Limitations to 1-Wire Communication Speed
Generally speaking, there are two primary factors that affect the design of a one-wire bus.

The first is the edge speed that you can get with the pullup device, which is usually a resistor, but sometimes enhanced with a transistor.

The second is the accuracy of the timing that each device on the bus can maintain. Most devices are single chips without precision timing elements (i.e., R-C timing circuits only), so the tolerances are rather loose. The bus protocol definition needs to take accomodate all of the possible variations in timing over process, voltage and temperature, and still have enough margin to maintain an acceptably low error rate.

Note that the WS2812 and related products operate on a 1-wire bus at roughly 800 kbps. In this case, the bus is unidirectional, which sidesteps the first issue.