Custom Teensyduino Keyboard

Hello guys.

I've pretty much always wanted to build my own DIY rgb usb keyboard, with a couple of lcd pushbuttons as custom function keys. The keyboard will be powered by a Teensy 3.6. Or the new 4.

My only hiccup is talking to the PC. I've toyed with KeyboardController in the past, sending the keys to the PC is no biggie. The problem is the PC talking back to a standard keyboard.

I've read online that you can include a custom field in the usb descriptors.
I'd be very interested in using a solution like, say a 8 byte report, in place of normal serial communication - many places I've worked at block com ports, for example.

Is it doable?