EUCON can be implemented in any DAW at no cost, which is why Cubase implemented it. It’s a feature of Cubase and part of the reason I bought a Cubase license in the first place. It would behoove Steinberg to completely ignore improving their implementation since this helps sell Cubase licenses.
The only difference between EUCON and Mackie/HUI is that anyone can make a Mackie/HUI controller, but only Avid can make EUCON controllers. Any DAW is free to implement EUCON as a protocol. Seems fair. EUCON support can be a mutually beneficial relationship: helps Avid sell hardware, and helps DAWs sell licenses to people who want to use said hardware.