@PaulStoffregen  - Not sure if this helps you or not, but thought since I had updated my excel with the  pin information for the not yet announced MicroMod, that I would add the data for Wire3.

Note: I  can obviously not test it as don't have one, but it does compile and still compiles for T4 and T4.1

They are both on the SDCard pins, but on T4 these are 36 and 37
whereas on T4.1 it is on 44 and 45

Verified it worked using Adadfruit_SSD1306 example sketch where I rn the different pins for both T4 and T4.1

https://forum.pjrc.com/threads/58654-Teensyduino-1-49-Beta-2?p=223880&viewfull=1#post223880

This appears to resolve the hang in the BNO055 test cases.

Basically I detect if the FIFO queue is not empty when you start these two functions and clear it out if it does.  Also NEED to then clear out the FEF status bit after you clear it.

You might want to see if there is a better way.  But @mjs513 said it also resolved his issue with MPL3115

T4 has alternate wire pins on the SDCard pins, which may come in handy in some cases.

So converted the pin initialization stuff to be close to what I did in hardwareSerial, and created a pin definition structure with pin numbers, and then mapped those pins to underlying IMXRT data...

Implemented setSCL and setSDA.

Tested with  modified version of Scanner.ino, and found prop shield devices on Wire, Wire1, Wire2 and then Wire1 on alternate pins...