If the framework is carefully written to be cross platform with OS-specific libraries linked in at build time then there should be no problem porting the game to another OS. All that would have to change are the OS and architecture specific libraries with the game engine and data pretty much untouched
In my opinion Carmack has used Linux to advertise their good will about it. I think the has not been completely sincere on his will towards Linux. Aside it he hasn't been interested in Linux since it wasn't a comercial platform.
Sorry Carmack, I believe you aren't sincere.
Hmmm... for me the most interesting is that ID policy for Linux was changed, when ID was bought by Bethesda Software (this company never cared about Linux). I hope that drop support for Linux isn't just of JC decision, but mostly Bethesda.
Wait, how many Linux games has Valve released to date? None? 100 points!
Wait, how many free Linux games are based on open-sourced ID code? A great many? 100 points!
Wait, how much source code has Valve released? Not much? 100 points!
Perhaps it's easier for Carmack to blame the platform instead of the plotless, derivative, unimaginative games iD churn out to what are basically tech demos, for those who don't appreciate gameplay.
There's plenty other games on Linux that have sold more (take Indie Game Bundle) than iD games simply because Linux users know the difference between shit and shinola :-)
He isn't in the same league as Valve, to quote them - Valve's games are imaginative, fun and playable. There's the difference - iD never made a game like Portal; Valve has, and more - their artistry shared amongst indie developers throughout the world.
I am a bit disappointing to read these harsh comments about what he said. If you listen to this speech and others he has done in the past it is clear that he loves technology and has pushed to get parts of their code to be opensource because he likes getting a discussion about it. In this speech you can clearly hear he is a bit sad that they have to lower priority on some stuff because Rage took too much time for them to produce and was not enough of a hit. They need to move their developers to focus on one thing in order to get next game out faster, this also means they are moving away from mobile development that he also said he loved doing.
He talks about the driver issues they had with Rage that caused bugs in their game and was out of their control. And later when talking about Linux he praised Intel for their opensource driver and said if he had more time he would love to do optimization work in the opensource driver. But with his rocket hobby and now the virtual reality stuff and his day job I can understand he does not have a lot of time left.
Give the man a break he has contributed more than most people to the linux gaming community and deserves a lot of respect for that. Btw while talking about valve pushing for linux he mentioned that in the beginning they thought the idea of them having doom on steam was crazy but they were proved wrong by valve so to me it sounded like if valve gets something going they would not afraid of joining.
Moreover, from this:
"Mac development is getting a boost at iD. John feels that it is becoming a much more important, and untapped space. Several factors have pushed iD in this direction. First off the hardware is now good enough overall for gaming. The latest Intel processors have a graphics portion that is entirely able to run games at decent resolutions and quality settings. We also have development houses like Valve actively producing titles for Mac and having robust Steam support for the platform. While there are no announcements about titles being ported to Mac so far, it will be coming."
So basically, from his point of view, a platform isn't a gaming platform until iD make games for it. Yeah, like Blizzard, Valve, Epic (etc) and countelss others haven't made great games for Mac years ago.
Thing is, look at their planned releases. Again recycled versions of past failures. This echoes an endemic problem with them that likewise must have affected their outlook to Linux - they haven't been and no longer are able to spearhead innovation in areas other than eye candy.