A reworked engine, especially in the way of pathing, responsiveness, and in the case of HotS, collision. The basic movements between these games are just different.
If you’re just talking about abilities, I can’t speak to HotS, but I can for DotA. In that case you’d need to remove orb stacking mechanics and buff placers and make them independently assignable. Vamp aura affecting ranged units, customizable interactions and bug fixes for effects like ethereal, as well as a slew of abilities that would be difficult if not impossible to implement.