I think there are FreeBSD people working on getting it into base. I know people have replaced the base OpenSSL with LibreSSL on their own.
Edit: This is not the case as feld has pointed out below.
Edit: This is not the case as feld has pointed out below.
By the way I actually do use client certificates on my home server. It's behind my ISP's NAT though, no incoming connections from outside are possible lol