I think this says more about Id's confidence producing a good mulitplayer experience than it does the viability of it. While I agree old-school deathmatch is not popular anymore, all you have to do is look at the success of Call of Duty, CounterStrike, Battlefield, etc. to see that there is a huge demand for multiplayer shooters.
When's the last time I cared about an Id multiplayer shooter? Would have to have been Q2 and that was only because there were so many good multiplayer mods. Their mindset has been to create good engines and let players figure out how to make it fun and that just doesn't cut it anymore.