Here's my initial list concept for my 6th edition Tyranids. This list has a focus on trying to get a survivable anti-flyer unit onto the table where it can maneuver to challenge enemy flyers and put some early pressure on the rest of an opponents army.
The Swarmlord with 2 tyrant guard (telepathy powers, gunning for invisibility...hallucination is a bonus though)
2 Hive guard
1 solitary hive guard
The Doom of Malantai in a pod
2x 10 gaunts
2x tervigons (single psychic power, and I'm just taking a crap shoot on biomancy powers)
This takes the list I've run successfully towards the end of 5th edition and switches up one or two things for 6th, taking advantage of the new psychic powers. The swarmlord is a psychic monstrosity, with access to two really powerful telepathy powers - invisibility and hallucination. You can't rely on getting these, but if you stubbornly refuse to trade the primaris power for a bad choice you have a 60% chance of getting the power you want, and also a 60% chance of the other good power. On a good evening, like yesterday, I end up with both. What invisibility means is basically a 2+ cover save for your flyrant, so even if you get first turn you can place him on the table, jump forwards into central cover, and camp out for enemy flyers to arrive. If you don't swoop, you don't have to worry about grounded checks and with luck you'll soak up whatever shooting there is... with even more luck you'll be able to cast iron arm or endurance on your flyrant. He should stick around... and you do have the option of swooping and combining invisibility with jink and ground cover if you think weight of fire won't bring him down.
Phase two of the battle plan kicks in on turn 2. With the Swarmlord's reserves bonus, there's a great chance 2 Trygons and the Doom will be dropping into a sensitive location somewhere near the enemy. The Doom has received buffs from the cover save and wound allocation, and was pretty deadly last edition - he's the one model that can really do damage the turn he deep strikes and takes advantage of reliable scatter free arrival in a pod. The trygons also can pop up pretty much wherever they like, and now they don't get hurt by dangerous terrain and receive cover from area terrain they'll be even harder to shift. Bonus... now if they fail their synapse check they get an additional attack, but they really don't need it. Trygons still kill pretty much everything they hit, and hit pretty much anything they can wildly swing their pointy bits at. So if the invisible flyrant is still alive, there's a lot of angry tyranid monstrous creature that needs to be dealt with on turn 2 before it takes the enemy army to bits.
So... once the enemy has dealt with all those T6 wounds in cover or bounced some high strength shots off the Doom's warp field... they still have the Swarmlord and two Tervigons, along with fifty or so spawned gaunts to shift off the objectives. Gaunts have some spectacular boosts to their blocking and tarpitting abilities in this edition and Tervigons have also gained S10 AP2 smash attacks to open up any land raiders silly enough to challenge the tyranid spawning grounds. It's not going to be an easy army to beat... and I'm sure I'll be able to refine it a little over the course of the next year or two.
I needed an excuse to start a new tyrant project, so here's the terrifying work in progress that caused a power outage on the whole block around my FLGS in downtown San Francisco last night. Alternatively you could blame the power outage on Pacific Gas & Electricity, but playing 40k by torchlight was definitely a novelty.