I searched my lube library (I am an ME and was a tribologist, currently IT Director for R&D at a Fortune 8 company). Here is what i found:
1) A US Army study of Slick-50 that found it did not do what it said, and actually increased wear in the cam lobes. It indicated the product should not be used in any internal combustion engines in the Army motor pool.
2) PTFE breaks down at high temps
3) PTFE can migrate under heat and pressure
4) PTFE is an effective dry lubricant and that is where it is best used, such as in space equipment and open gears/rollers
5) When burnt, it forms a corrosive and toxic product.
6) It is chemically inert and resists oil - why would you want that in most areas of an engine? It can be used on piston skirts, con rods, and rocker springs because it resists the accumulation of oil, which in a racing car has benefits, much along the lines of a windage tray.
7) There are no scientific studies I have seen that indicate PTFE colloids will "plate" anything - PTFE plating for the arm of the Space Shuttle is done in a clean-room environment.
8) Moly has a much higher film strength - PTFE does not.
9) I found a gear company that makes a big deal about applying a PTFE coating to its ring and pinion gears. This makes no sense, esp. since the EP addtives in GL-5 gear oils are designed to work on and into the metal, and the OTFE would interfere with that process, leaving only the PTFe trying to cope with high loads - it cannot.
etc, etc,