Conductivity has been a talent that is hardly ever chosen by any Shaman, since it also shares the talent tier with Healing Tide Totem and Ancestral Guidance, both which are pretty powerful. But Blizzard has completely redesigned Conductivity to be more interesting, however Healing Tide will probably still be the strongest contender for that tier talent.
Conductivity has been redesigned. Casting Healing Wave, Greater Healing Wave, Healing Surge, or Chain Heal, increases the duration of Healing Rain by 1 second. Damaging an enemy with Lightning Bolt, Chain Lightning, Earthshock, or Stormstrike increases the duration of Healing Rain by 1 second.
If this means Resto Shamans could keep a perma-rain down it could get some use. However we need to be able to test this on the PTR to know if it can be a perma increase, or if it can only ever be increased by 1 second per Healing Rain dropped. Sometimes Blizzard mangles the tooltips.