The owner of a taxi licence has a Constitutional property interest in the licence, but not necessarily in its economic value.
Sufficient rational basis for treating street-hail cabs differently than app-based services.
City's licensing scheme does not use language that plainly expresses the intention to create a contractual obligation, and is not definite enough to bind by estoppel,.
http://www2.ca3.uscourts.gov/opinarch/171358p.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.