[EliAndrewC]

There are a lot of middle-ground options, such as "buying back" taxi medallions before opening the floodgates and letting anyone run a taxi. This is obviously a tricky approach for a lot of reasons, but certainly there's a middle ground between "taxi medallions forever" and "all taxi medallions are worthless overnight".

[InclinedPlane]

Having a competing service like uber is actually precisely that middle ground, since taxi medallions are not worthless overnight.