I was having pretty much the same thought myself.
Why would you want a 64-bit processor on a phone?
The answer right now is: A processor with the ARMv8 ISA will be more powerful per clock and draw less power per clock and use less transistors per area than the previous ARMv7 would allow. It'll be a cheaper, faster and less power consuming than its predecessors. THAT'S the reason. Let's do it. Oh, it'll be 64-bit with no drawbacks too since we already have all the software tools and knowhow to make the leap, so let's do that too.
Install Linux. Cost $0 + admins' time -- almost certainly less than trying to remove and clean infected systems.
+ cost of education of the IT staff
+ cost of education of the users
+ cost of reduced productivity for the users and the IT staff until their competence rises to the before level.
Since they already had licenses for Windows, it'll cost nothing but time to re-install Windows. In that scenario, education of the users is zero, and there will be hardly no production loss for the users. There should be some money left to educate the IT staff to handle mitigate the virus threat on their chosen platform.
have a die shrink down from 45nm?
Probably not. I haven't heard any word on further development of the Cell BE-processor beyond the 45 nm node. Nor for its cousin, the PowerXCell 8i processor. Sony could probably enable the 8th core though, yields should have risen considerably since 2008.
What the gods would destroy they first submit to an IEEE standards committee.