ARM announced that they will release 64bit microcontrollers. The ARMv8 uC will feature a 64bit instruction set, as well as extended virtual addressing. The uCs will have two execution states, AArch32, and AArch64. While the AArch64 handles the 64bit instruction set, the AArch32 executes the existing ARM 32bit instruction set.
A compiler for the new 64bit instruction was already developed, and open source support is promised.