Hello, as MS already entered to the world of Win32 Arm64 applications (DISM.EXE on picture below), here are the differences in file headers: Architectures are as follows: x32, x64, i64, a32, a64 Officially marked as: x86, x64, ia64, arm, arm64 BTW: Would you like Windows RT 10 a64?
How could that question be answered (yet)? As long as there not any developers producing 64bit App's why shouldn't there an need for a 64bit OS? Look at the developments of 64bit apps for the 'normal' desktops! Till now about 80% of the new developments of software is still 32bit based! How often MS has announced the they will stop with the development of 32bit OS'es for to push the development of 64bit apps? And what's the result? Take all in consideration, there isn't any need of an 64bit ARM OS!
The reason why there are still so many applications 32-bit instead of 64-bit is that they are pretty happy with the limitations of a 32-bit processor. The single biggest advantage of a 64-bit processor is the larger address space, but there are actually not so many applications that really make use of it or need it. On the desktop side, this is mostly multimedia-related stuff (audio/graphics/video processing) and games, all applications that have to deal with huge amounts of data, but the big remaining portion is just OK with the 4 GB limit. Therefore, it doesn't make sense to drop 32-bit Windows client releases just yet, because there is actually still demand for 32-bit software, even in 2015, especially on small devices with less than 4 GB of RAM where a 64-bit OS doesn't give you any advantage at all. Right now, there is no need for a 64-bit ARM OS, but maybe it's a good idea to be prepared.