On any special based set HP fighting looks increasingly attractive as it hits nattorei and empoleon, 2 of the 3 pokemon that resist kingdra's stab (and who uses shedinja?), who would normally cause problems for kingdra.
Set 2 Really should have Boiling Water over surf IMO, as when you're locked into it, it'd be nice to get the 2ndary effect if you hit whatever tries to revenge-kill it. A burned electric or grass type is not a bad thing...
I was thinking a set as this:
Kingdra @leftovers/life orb/lum berry
Damp/Swift Swin
damp is nice to prevent you from explosion when you trap something and swift swin can benefit of some rain of politoed^^
adamant 252/252/4 atk speed HP
or any spread that you like
Whirlpool
Dragon Dance
outrage
waterfall
basically you can trap something that can't damage you much and start using dragon dance to become really strong.
leftovers for more surviability, life orb for extra damage and lum in case you are worried about status.
Alternatively, you could run Kingdra with Politoed's Drizzle, and just use Sniper instead of Swift Swim (since no one wants to run Damp). It lacks the insane speed it once had, but it's still bulky, insanely strong, and can carry a Scarf to help its Speed. I don't know if it would work well, but it seems worth a shot on Drizzle teams.
...also, you'd kill basically anything if you get a crit.
Kingdra is too slow this gen to go without speed boosting. What with Rain effectively being neutered, this means DD sets. Skarmory walling ahoy.
RD Kingdra? Cool. I love wasting a turn for when random Sand Streamer comes in like you know they will.
It's wasted set-up considering it only lasts 5 turns. You're better off using something more lasting.