I tried out CopperheadOS earlier this morning. The encryption password/pin combo was working, although I ended up flashing back to stock nexus so I can install Signal again.

It's listed as abandoned, so it doesn't look like the change is going to be upstreamed: https://android-review.googlesource.com/#/c/154841/ (also in article)

Is it just me, or is that page awfully quiet?