This is quite a large technical undertaking, with a very small pay-off given the tiny percentage of users who develop on their Mac for iOS devices. I can't see this being something that happens until x86 CPUs have been removed entirely.
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.
If the model trend continues to grow as it has been since the iPhone 6, there might be actually a need for device model emulation for development...
https://en.wikipedia.org/wiki/Samsung_Galaxy#Phones
That's just one manufacturer.