On the one hand, that would be better for me, because the way my desk is laid out to plug in my headphones on my iMac I have to reach under the front and jumble around blindly.
Having the headphone jack on the left side would be easier.
On the other hand, someone with a second monitor that prefers it on the left might find that it is in the way of their headphones.
What I really wish they would do is make it so that you can keep your headphones plugged in, and choose via the Sound settings whether you want sound to go to them or the internal speakers.
EDIT: My iMac is a 2017 model. From what I've read elsewhere, they may have changed the behavior described in the "What I really wish" paragraph in later models.