Compared to the Wings of Liberty and Heart of the Swarm campaigns, the scout is more fragile and has a weaker anti-air attack, but has a much stronger ground attack. Though they cannot be built, Dark Archons can take permanent control of enemy scouts.
The Scout's design for Wings of Liberty went through several phases, as while its new design was to have homages to its original form, designers had different features they liked about the original. Another concern was making it look more organic in accordance with the protoss units in StarCraft II having more flowing shapes and fewer geometric angles. A design was finally settled on, with the StarCraft-esque wings being replaced by more organic looking ones.
Incomplete tooltips for the scout imply it may have been intended to be usable by the player in the StarCraft II: Legacy of the Void single-player campaign. These tooltips imply the scout would have been a purifier faction unit, and have an Afterburners ability that boosts its speed.