I got a hold on the new style of trackpad (started in 2016, I think) and the board schematic for a matching macbook pro. It looks like they moved to SPI for the trackpads, so I think you’d need to add another controller to convert it and at that point I don’t think you get the driver support.
Here’s some info for anyone that wants to pick up from here.
Interesting chips on the trackpad:
* BCM5976C1 - There’s 2 and I think this is the digitizer and I think it’s i2c
* STM32F103C8I6 - Arm Cortex-m3, capable of USB but IO is software controlled I think
Here’s the pin out for the trackpad connector on the logic board (I think you can ignore the KBD stuff since the keyboard uses a different connector):
# SMC_LID
# SMBUS_SMC_3_SCL
# SMC_PME_S4_WAKE_L
# SMBUS_SMC_3_SDA
# SMC_ACTUATOR_DISABLE_L
# KBD_INT_L
# TPAD_SPI_INT_L_CONN
# KBD_I2C_SDA
# GND
# GND
# TPAD_SPI_MOSI
# KBD_I2C_SCL
# TPAD_SPI_CS_L_CONN
# KBD_BLC_XBLANK
# TPAD_SPI_MISO
# KBD_BLC_XBLANK
# TPAD_SPI_MISO
# KBD_BLC_GSSOUT
# TPAD_SPI_CLK_CONN
# KBD_BLC_GSSCK
# PP5V_S4_TPAD_CONN
# KBD_BLC_GSLAT
# SMC_VIBE_L
then everything else is power or ground (5v, 3v, 0v - active gnd, 12.6v on a fuse)