They're already talking about using EGS specific features. With their user hostile approach to everything EGS, I doubt you'll keep the same experience on Steam.
Do you have any sources for EGS specific features? I really don't want to speculate because I really want to root for Psyonix here, but this is what I'm afraid of. New maps and queues only being available on the Epic version, being able to purchase/unlock DLC/items on the Epic version only etc.