After #3184 is merged, there might be something left for OpenBSD support. Since navigating #416 is by now impossible, I've chosen to close it. Let me paste here this TODO list from @borsboom (#416 (comment)):

Steps remaining for official OpenBSD support:

• Have stack setup use bzcat/xzcat to uncompress GHC bindist instead of relying on tar to do it (see also stack assumes tar is GNU tar, but that's not always true #2283)
• Await a Stackage LTS snapshot that uses GHC 8.0.x and update the Stack build process (and integration tests) to use it
• Ensure integration tests pass
• Integrate into release process (I've already added a starter Vagrantfile in etc/vagrant/openbsd-5.9-amd64/Vagrantfile)
• Perhaps remove old not-quite-working OpenBSD bindists from stack-setup-2.yaml, to avoid confusion.

EDIT:
Status: install should at least work for GHC 8.2.1 on OpenBSD 6.1, now that commercialhaskell/stackage-content#25 and #3184 have been merged.