I just tried it. :X asks you to enter an encryption key, then asks you to enter it again, and only continues if the keys match. And then you're still in vim and need to save your file to overwrite anything. Seems hard to do by mistake.
> I am not sure ARMv1 (and v2) even had supervisor vs user mode, etc.? (It may have, Google isn't helping me here)
v2 at least had 4 modes: user mode, supervisor, IRQ and FIQ. They were encoded in the low 2 bits of r15 (which weren't otherwise needed, since the PC was always word-aligned).
The original Archimedes was intended to run a "preemptively multi tasking, multi-threaded, multi-user, written in Acorn-extended Modula2+" system called ARX. But when that wasn't ready in time, they ended up just porting the 8-bit BBC Micro MOS to the new 32-bit machines!