Keeping a simplified menu is going to be something of a tug of war between McDonald's Owner/Operators and McDonald's management. There will be three forces pressuring management to slowly return to a more complicated menu and operation.
1) Investors and analysts - If management doesn't produce a stream of new products, they will be accused of not having an "Innovation pipeline". If the company ever returns to having in-person "analysts' days" the guests will expect to be fed exciting new products from that pipeline.
Investors will give a simplified menu lip service, but they don't understand what it means and will reflexively push for menu creep.
2) Industry media - Reporters need content and clicks so they will write about any new product news they can find. They will constantly bug corporate about new products. I'm amazed how much press Shamrock Shakes are getting. Can a 40-year-old product be new product news?
But the Chicago office will contribute to this pressure from the media by cranking out press releases about new products, especially when they need positive press.
3) Social media - "Listening to our customers" is an oft-used phrase. Unfortunately, sometimes that means a marketing person spending an hour on Twitter and Tick Tock. A few comments from a few people (McDonald's customers or not McDonald's customers) and "the Internet is on fire" with people demanding fake meat or ADB.
Exactly how this tug of war takes place will depend on same-store sales. If sales stay positive in the USA there will only be muted cries for new products. If sales go soft or McDonald's USA falls behind the competition the outside pressure on management will be substantial. And, with so little real restaurant experience in Chicago, it's likely management will easily yield to the pressure.
Only Owner/Operators can prevent menu creep.