We would love to merge in Konstantin's ASLR work. Reviewers have pointed out performance issues and memory fragmentation issues, especially on 32-bit platforms, but it's still better than nothing. I think we should just merge it as is, maybe default to off on 32-bit platforms, and improve from there. With the intent to have it polished for 12.0-RELEASE.
One such mitigation receiving community attention is Capsicum. The Capsicum security sandbox is a viable way to constrain applications. Unlike OpenBSD's pledge, rights are limited on a file descriptor basis. It has been ported to Linux and DragonFlyBSD (although merged to neither). There has been a lot of work in FreeBSD lately to restrict base programs, especially setuid programs, using Capsicum.