Sarcasm aside, the 295x2 got away successfully with a single 120mm radiator, dual pump setup. It'll probably be the same on a dual Fiji card. Besides, Fiji is more power efficient and as or less power hungry than Hawaii, it'll work out just fine for them. The only problem would be whiny pumps, I suppose they got that one figured out by this time, but as always you can't expect logical results out of AMD. Anything could happen.
The issue here will be if nV tries to cool 2 GM200s with a heatsink + fan. The Titan Z was a throttle fest. Titan X already struggles with that on the reference blower. 2 of them in a single PCB will definitely be a problem on air, if that cooling solution gets repeated. Titan Z GM200 < Titan X SLI < properly cooled TX SLI, as a result.
On the other hand, 295x2 was equal to or better than *aftermarket, low GPU temperature, throttling free* 290x crossfire (reference blower of hell 290x crossfire doesn't even come close here) because of it having proper cooling. nV has to make the jump to a superior cooling solution sooner or later, especially when designing this kind of sli on a stick cards.
Still, I'd prefer something between the 960 and the 970 instead of a niche product like a dual GM200 card. Further cut down GM204 could fill that void, but I don't suppose there are so many significantly failed GM204s to do that without cannibalizing healthy ones.