With Gergo [2] I took a different approach, and opted for every key to have pads for connection to the i2c bus, as well as a custom footprint for mounting devices (Needed as I2C is slow and that footprint is connected to a interrupt-able bus). That allows me to create stuff like PCBs cast in resin, vibrating keys and whatnot and whack them around the board, but there is a single slot for anything that needs quick feedback. When a board is 1x1.2cm, you only have so many options, and burying it in resin is valid.
But if you want to have a unified device, you pretty much need a firmware that can handle it. QMK is an amazing project if you've never seen it. It powers Gergo, drives the Trackball and communicates with my boards. And it's open source! Feels weird to be writing and flashing keyboard firmware, but it's crazy useful.
Threw a few more images here if you want to take a look at the module [1]
Make an own keyboard controller.
It also be very nice if it can actually handle trackpoint as an actual joystick (real trackpoint is a tensometer, not a position sensor.)