As I continue to look through the new Genestealer Cult rumors, I think more and more that they will be a very solid, competitive army, especially in the hands of a skilled player who can maximize their special rules, wargear options, and unit choices. Since Craftworld Eldar are generally considered the most “powerful” codex out right now (with Tau right behind them), here are my initial thoughts on how the new Genestealer Cult army can counter the Space Elves:
 Webber weapons — These are new (or “rebooted” old, really) weapons that Genestealer Cult units have access to. Web Pistols are S3, Webbers are S4, they are both Assault 1, Small Blast Weapons whose AP is determined by the the strength of their target… if a target is S3, for example, then they are AP3, if it is S4, they they are AP4, etc. Given that the entire Eldar Codex, except for Wraith constructs, Phoenix Lords, and the Avatar of Khaine, are S3 and have 3+ saves or worse, this makes Webber weapons very effective against almost all Eldar non-vehicle units. I think they will particularly shine against Eldar Jetbikes and Aspect Warriors, as their S3/$4, AP3, and multiple Small Blasts can really put out the wounds.
 Purestrain Genestealers — This guys cost the same as “normal” Genestealers from the Tyranids Codex, but are better in multiple ways, including coming stock with Stealth, 3A base, and a 5++ Invul Save. They also get access to the Cult Ambush and Return to the Shadows rules, which makes them MASSIVELY more dangerous; about the only advantage “normal” Genestealers have is Objective Secured in a CAD from their Troops status. Additionally, Purestrain Genestealers gain Furious Charge if they are joined by a Patriarch. Taken all together, especially with the potential to get VERY close to enemy units (and even possibly assault the turn they arrive, if you are lucky) when arriving from Reserves via Cult Ambush and the ability to go back into Ongoing Reserves and “rinse and repeat” via Return to the Shadows, and you have a truly deadly assault unit (their massed WS6 I6 Rending attacks will even strike faster and better than most Eldar) who can actually catch the mobile Craftworlders and tear them up in combat (i.e. 15 Genestealers with Scything Claws upgrades get 75 attacks on the charge, about 50 hits, 8-9 Rends, and about 6 Unsaved Wounds on a Wraithknight after FNP rolls, all before the Wraithknight even has a chance to strike).
 Broodmind Powers — With the ability to nerf Eldar stats (i.e. Mass Hypnosis), hurt them with solid Witchfires (i.e. Psionic Blast or Mental Onslaught), or buff friendly units to be even more dangerous (i.e. Psychic Stimulus and Might from Beyond), especially when charging out of Cult Ambush arrival or a friendly Goliath Truck, this discipline can work very well against Eldar in the hands of a Patriarch and/or Magus. Even better, if you roll up Telepathic Summons you can keep bringing in more free reinforcements (with free upgrades, to boot!), but the best is Mind Control. If you manage to get this ability off on a unit of enemy Wraithguard, Scatbikes, Warp Spiders, Dark Reapers, Fire Dragons, or Dire Avengers (or even an enemy Wraithknight with dual Heavy D Cannons), you can turn the Eldar player’s potent firepower against himself and potentially even change the course of the game in a single Psychic Phase.