The current one is already very good, as is the 85. So I would bet not for a bit. Most of their lineup needs a redo before those do. If they do something to it, expect them to fix the AF QC and just repackage them, they are optically good.
Think about this, there's a ton of stuff in their lineup that needs updated first:
--The 28 1.8, 24 1.8, 20 1.8. Those need updated really, really, badly. So badly. lol. They are an embarrassment.
--The 10-20 lineup is pretty good but could be simplified to one lens. They have no FF wide angle that takes filters, either, that needs fixed. The 12-24mm is good and the 8-16mm is superb, I'd expect to see those turned into the new style later though, round the same time as the 50 lol.
--The 24-70 2.8mm needs a makeover. They could remake it with their superb new glass and make it kick butt, it was released before that FLD stuff came out and needs a makeover long before the 50, probably.
--The 70-300 Sigmas are uhh...rather crap, honestly. Those need updated something awful. Second only to the wide primes, let's be honest here. These are also an embarrassment to the brand imho lol.
--The 150-500 and the 120-400 (less so). Let's be honest, optically these don't match up to the 50-500, not even close imho. They really need an update. Speaking of the 50-500 OS, it just needs a focus limiter and that's it.
--The 300 2.8, 500 4.5, 800, and 300-800. Those need updated something awful. They need OS. Bad.
--The 50mm macro and 70mm macro really need HSM, but optically they rock, so it's not as critical as the stuff above, they also don't really need OS. So just HSM + new packaging. I'd put these at the back of the list.