The problem with Windows 10 (and Windows 8) is that it requires the NX bit be present on the processor. The NX bit came in around the same time as Intel was making the transition to 64-bit, so while there are a small handful of 32-bit processors that can run Windows 10, the vast majority of 32-bit Windows 10 systems are going to be running on 64-bit hardware because it won't boot on most 32-bit systems. So while you can run Tails (for now) on that Socket 478 P4 or Athlon XP, you can't run Windows 10 on it, even if the hardware is otherwise powerful enough.
Also, as far as I know the requirement for signed drivers is only for 64-bit Windows. Which makes sense, as the 32-bit version of Windows 10 is basically the "compatibility mode" version of Windows that you can try to use for all that old, crufty software and hardware that simply will never work on 64-bit.