It would be nice to have this stabilized at least on x86, because the current stable version doesn't work at all on x86 hardened (bug 344031).
This is NOT happening yet. The problem is that the hardened fix breaks multilib under certain conditions, and we're still working on that.
Current stable MySQL also has a very nasty innodb bug that fails CASCADE DELETE foreign key RI rules: http://bugs.mysql.com/bug.php?id=57255 I suggest marking 5.1.51 as unstable until 5.1.53+ is ready.