it is a stretch to say A6 will be based on ARMs A15 core. Apple could just as easily shrink the current design and add a couple of more cores. At 28nm they could go to four cores, up the clock rate and still be ahead on power.
Beyond that A15 IS NOT 64 BIT. Apple will need the 64 bit address space sooner than many think.
There is some debate going on about this.
Oddly, your comments regarding what is hard to follow, are unclear. Making some assumptions, on what arguments you find unclear, here are follow up comments.
Given the progression between Apple's mobile core designs, I think it's reasonable and generally speculated that the A6 would be based upon the ARM A15. The mobile SOCs seem to be a step or two behind in terms of fabrication density, so a move to A15 is more likely than a move to 28nm. The current speculation is that Apple would push to 40nm with a chance of 28nm versus the current 45nm. I think it's far more speculative to say that a change in core count + change in fabrication by 2 steps + change in clock rate > A15 + change in fabrication by 1 step with respect to power and speed. A quick look at the history of ARM cores shows a marked improvement in performance/watt with each subsequent generation. The move from A8 to A9 resulted in a DMIPS/MHz improvement of 2 to 2.5 or 25%. There was a similar improvement moving from the A5 to the A8, so it seems reasonable to anticipate a similar improvement moving from the A9 to A15. Given relatively low operating frequencies of mobile chips, and the direct relationship between frequency and power, it seems more sensible to move to a more efficient core.
Apple to move ARM SoC production away from Samsung in 2012
ARM Cortex-A Series
With respect to the requirement for 64-bit address space, that requirement is only now beginning to exist on the desktop and even then, only in limited areas. When system memory on the iPhone/iPad/iPod is still <1GB and hasn't changed in 2 generations of product, it seems a bit much to suggest that 64-bit is much of a priority.
As for your final comment regarding "some debate going on about this", it's not clear which statement(s) you are making referencing.