I tested 1.60 with PlatformIO (manually), and the original branch of MTP_Teensy still requires setting the LDF mode to deep. It is no longer needed with pauls_branch. This branch compiles well with 1.60 (with just two unused variables warnings...
Until 1.60 is released on PlatformIO (I can confirm, as @wwatson said, that pauls_branch won't compile using a version of the core library prior to this commit), it seems that changing the Library Dependency Finder (LDF) mode to "deep" in...