I think that matching a Titan may be a tough ask, unless AMD are willing to produce a >6Bn transistor, 500mm^2 chip (which they have historically been reluctant to do). To do so would seem a lot of work for a relatively short product cycle.
I think the key will be the clockspeed; how stable the shader-pipeline process can be made. If AMD can add 25% to the SP count (for 2560 SP), and can *also* manage to up the core clock a little (always a tough ask when increasing die size), perhaps closer to 1200Mhz, then we could see it happen. Realistically though, I'm expecting the chip to fall a little short of Titan performance, though matching a GTX780 is not unlikely.
I agree with you that a sub-Titan performing chip is unlikely to persuade high-end enthusiasts to upgrade from their existing 28nm setups. I certainly wouldn't upgrade from a pair of 7970s under water either...
I still don't think Tomb Raider is a good benchmark to be judging the relative performance of cards though - it doesn't reflect the overall picture particularly well. Metro Last Light should give a better indication of relative performance, and Heaven 4.0 seems to represent the overall picture fairly well as well.