This article is basically irrelevant. They asked a bunch of devs what they thought of mantle at a nvidia convention. What do you think they are gonna do, badmouth them at their own event?
"If you'd ask me if I'd much rather have a low level API for accessing the GPU, the answer is yes. But five of them, for different hardware, vendors and operating systems? Absolutely not."
It's obvious that Carmack has been out of the game for awhile. If a company has time to implement PhysX, TressFX, proprietary SSAO and AA, and other tech that only works on one card type, then they definitely have the time to implement a performance api. I guess he really should have said "Only if we get paid a little extra on the side". These APIs are optional, amd doing this has no effect on anything if a dev decides not to implement this. Even if Nvidia were to come out with their own api, devs can choose to use neither.
I don't know why someone would even ask these questions in a nvidia convention. It's like going to a republican convention and asking them for their opinion on a new democrat based bill that extends the government.