Well, id's GNU+Linux support never was stellar. You had to download a binary from a hidden webpage, and copy contents from the DVD of the Windows version. After the copy finished, you could execute the installer that didn't install all the libraries needed, so you had to use manually your package manager to install those libraries if the installer asked for them. But at least you could play.
Then, they launched Rage which had a lot of bugs in their initial release.
Probably id Software didn't support GNU+Linux during the best times, but now is a wrong moment to stop porting games to it. They should put more money into it. I don't understand what Carmack means with "good will". GNU+Linux users are buyers like in other platforms, and I have to say that GNU+Linux buyers were treated worse than other platforms.
All I can see here is that id Software has become a small studio and that kind of companies have two options: launch Windows only games (cheap) and sell enough units, or be an exclusive of a determined console platform (cheaper than being multiplatform and easier).
Valve's approach is a bold one, with a lot more effort than id Software. And "Steam Play" games sure will be ported in the long run, some buys I made in the latest sales were based on that possibility too.