Capsicum, POSIX and NFS4 ACLs are all about adding complexity to allow for greater administrative policy enforcement. To put the OpenBSD point of view into perspective with a modern example, this is exactly the kind of policy that makes NSA admins rest easy at night and exactly the kind of security that allows Edward Snowden to secretly make out with 200,000 top secret documents. Real security means the software *does*what*it*promises* which a large and complex administrative policy enforcement system can almost never do.
In OpenBSD, security means that you eliminate bugs so that the most basic promise is held true. Adding complexity almost always does the opposite. We are talking about two completely different ideas of "security" here. This is not to say that ACL systems have no place, but rather, the systems that are smaller, easier to audit and easier to implement are going to find a place in OpenBSD long before the large and unwieldy systems could ever be incorporated.
That being said, FreeBSD 10 was the first FreeBSD system to distribute signed packages. OpenBSD 5.5 will be the first version of OpenBSD that distributes a signed base, signed firmware and signed packages. The code is small, the benefit is clear, and the implementation (at least in OpenBSD) is obvious.