We have been waging a long war against random proc stuns. We managed to clean up several of them when we changed mace spec, but like vermin, they sometimes crop up again. The Death and Decay glyph and Starfall with Celestial Focus were the two greatest offenders because they affect multiple targets. We will almost certainly be phasing out the single target random stuns (such as the Starfire stun of Celestial Focus and Blackout) as well. We didn't do that yet because it involves changing several talents and in some cases we will need to provide compensation.
I'm a big fan of blackout. (Didn't that proc rate used to be 15% by the way?) It's not something I'd recommend for raiding but it's a really neat spell for levelling and general grinding - and I'm sure it can be pretty powerful in pvp.
What we can expect to see in its place is uncertain. But if you're currently specced into this talent, enjoy it while you can.