My https://github.com/kinx-project/kint project is a replacement keyboard controller for the Kinesis Advantage keyboards, which allows you to use QMK :)
Yeah this is what I was going to say. There are a few projects which allow one to swap out the firmware for a custom one on Advantage Kinesis keyboards. There's one with a teensy, one with a custom controller. It's not exactly trivial to do, but I think it is the ultimate if you want to go that route. The hardware design of the Kinesis is top tier, but the software is a bit weak.