What if only ice poke get it will it get "banned" like Swim-drizzle?
Well, Smogon didn't ban Chorophyll with Drought and Sand Rush with Sandstream. I think Smogon bans Drizzle and Swift Swim because of instant 50% water attack and double speed in perma-rain. Since Hail doesn't offer any kind of power boost for Ice Pokemon, I would say Snow Warning with double speed ability in hail is safe from ban.
It is unfair for ice pokemon not getting any kind of defensive boost in hail. Let's look at the other 3 weathers. Rain makes ALL Pokemon gain 50% BOTH defense against fire attack. Same goes for Sunny Day in opposite type. Rock-type Pokemon in sandstorm gets 50% special defense vs ALL special attack. Quite powerful defense bonus for respective weather. Hail gets ... nothing. I hope in Gen 6 Ice-type Pokemon gets 50% defense bonus against physical attack, especially Rock, Fighting, Steel and some Fire attack.
I would love to see double speed in hail ability for Ice-type Pokemon and some non-Ice Pokemon like Empoleon. Ice Pokemon is known for slow speed. I was shock that Sandstorm gets Sand Rush and Sand Force, while Hail gets nothing. About 26 out of 31 Ice-type Pokemon's speed rating is less than 95 base. This includes all basic stage and alternate form. If exclude all basic stage and Uber, then 15 out of 18 Ice Pokemon whose speed is below 95 base speed.