Taylor brings up many valid points. For instance, when the most common trapper in the DW metagame has Fire STAB and the ability to OHKO Abomasnow right off the bat, how can you even deal with that? Of course a Shed Shell can somewhat mitigate this, but it's very problematic for those planning to abuse hail with BlizzSpam or any similar strategies. Another issue is the prevalence of Genesect. With Flamethrower and STAB U-turn, it's going to be doing major damage and there won't be much stopping it.
Again, quoting Taylor, stall is not very viable in such a fast paced metagame. There is just so much brute force behind attacks that stall won't even know what it was hit by. Let's look at rain stall as an example first, though. I have not seen a single rain stall team prepared for Manaphy--one of the biggest threats in this very metagame.
/B/utterfree brings up a good point, Magic Guard users are great for hail. One thing you should note about Reuniclus is its access to Trick Room, possibly the most anti-metagame move in DW OU. This is a tier ruled by Speed, but what if you could use the opponent's Speed against him or her? That would be wonderful, and Reuniclus is a prime contender for this. However, all Reuniclus have to fear the wrath of Genesect, so it should probably be advised to run Hidden Power Fire or something of the sort to ensure that a major threat to one's team disappears and so that Reuniclus can freely ruin the opponent.
However, even with these boons, I cannot see hail ever becoming viable in this fast paced DW metagame. Another sad thing is that the DW metagame is a theoretical final OU, meaning that if there is no major change in the metagame, hail will be in serious trouble. It's a sad, but undeniable truth, and we'll just have to wait and see how that folds out.