The BOOST plug is a "Power Functions 2" plug like those introduced with the WeDo 2.0:
The plug has 6 pins. I consider pin 1 the left pin on that image (just to be sure, if we see the plug from front, it looks like an inverted "U")
1 - motor power
2 - motor power
3 - ?
4 - ?
5 - ?
6 - ?
Between pins 3 and 4 my multimeter measures 2.2 KOhm, it seems the AutoID. For reference, we can trick the WeDo 2.0 SmartHub to use a common motor by connecting a 2k2 resistor between pins 3 and 5 and also connecting pin 3 to pin 6 (pin 3 might be GND and pin 6 an Analog Input)
Update: a 2k2 between p3 and p4 is not enough. Philo thinks there may be some handshaking through
p5 and/or p6
But WeDo 2.0 motors work and also just a 2k2 between p3 and p5 is enough to fake a WeDo 2.0
motor (no need for p3 to p6)