Historically, ARM really, really did not like unlicensed or open-source ARM processors. But times change, so I wouldn't be surprised to see them take some easy PR from openwashing at some point.
That seems highly unlikely - unless we're talking about 3rd generation behind the latest tech chips. I could see them open source say the ARMv6 architecture in 3+ years, when ARMv8 has already taken off, and ARMv7 is in legacy mode. But meh.
ARM would very aggressively go after any open source implementation of the ARM ISA. For the longest time you couldn't find any ARM documentation on the net because it was all behind a license agreement that read, "won't be used to make an open source version of our schwag"