It's really more like two Titans then two 780tis. But based purely on core count I'd agree with you.
He said if price doesn't matter. And the Titan Z is the top of the line right now (not saying it's worth the $ however)

It's not, really, for mining -- Maxwell's shift throughput is key for high performance in a lot of hash functions. That's why a multi-maxwell would be so awesome.
Can't wait to see what a maxwell version of the Tesla K40 or Titan line will be like for mining. Should be through the roof in performance.
Probably not for ROI however.