A comment on reddit by id Software co-founder John Carmack (thanks Develop) follows the theme of a recent post by former id programmer Timothee Besset indicating that id's once-strong support for Linux gaming has waned. The post basically confirms and explains that premise, discussing how he sees a plausible path for Linux gaming via emulation on Steam, if "properly evangalized," but expressing skepticism about commercial native Linux ports:

However, I don’t think that a good business case can be made for officially supporting Linux for mainstream games today, and Zenimax doesn’t have any policy of “unofficial binaries” like Id used to have. I have argued for their value (mostly in the context of experimental Windows features, but Linux would also benefit), but my forceful internal pushes have been for the continuation of Id Software’s open source code releases, which I feel have broader benefits than unsupported Linux binaries.

I can’t speak for the executives at Zenimax, but they don’t even publish Mac titles (they partner with Aspyr), so I would be stunned if they showed an interest in officially publishing and supporting a Linux title. A port could be up and running in a week or two, but there is so much work to do beyond that for official support. The conventional wisdom is that native Linux games are not a good market. Id Software tested the conventional wisdom twice, with Quake Arena and Quake Live. The conventional wisdom proved correct. Arguments can be made that neither one was an optimal test case, but they were honest tries.