I understand Part 15 (as well as Part 97, since I'm licensed under those rules). The mechanisms mentioned in the GP _do_ exist in law for 5GHz U-NII (read WiFi) systems. Please refer to Title 47 Part 15, Subpart E, particularly 15.407(h)(1) and (2) and also 15.37(e).
Also, (if I read it correctly) 15.37(h) forbids the marketing or sale of devices that use any digital modulation technique other than Spread Spectrum operating in the 5725-5850 MHz bands starting on June 2, 2016.
The definition of "digital modulation" is distinct from SS - from 15.403(f):
(f) Digital modulation. The process by which the characteristics of a carrier wave are varied among a set of predetermined discrete values in accordance with a digital modulating function as specified in document ANSI C63.17-1998.