If they go that way, the pay off obviously wont be "helping iOS developers have faster simulations", but as the parent already implied, beta testing and driving forward the eventual mix of iOS apps and macOS. So the "faster simulations" would just be a step in that process helping with perfecting it in a low stakes situation.

Plus, if it indeed happen, as the article also states, it would be used for another payoff, always on (at least when on mains power) Hey Siri, plus controlling the touch strip perhaps.