They will be using the same system as other melee strikes, which can hit mutliple enemies based on the animation. But that's significantly different from having splash.
This thread was added on June 01, 2019, with posts from Mark_GGG.
Original Post
https://www.reddit.com/r/pathofexile/comments/bvr29h/will_default_auto_attacks_have_splash_when_using/