Daniel Gilbert (Tall Dog on Tindie) has developed a breakout board that let’s you easily use Arduino shields  with the Teensy 3.5 or Teensy 3.6

This convenient board includes all parts needed to assemble a breakout board that allows you to connect a Teensy 3.5 or Teensy 3.6 to shields designed for the Arduino Due and Mega.  It features switches to select between USB or external power as one to set the US host port’s power mode (used for the Teensy 3.6).