Right now, very slim. It's not in line with how the US views antitrust, and there isn't any real demand from voters.

But it depends how this plays out in Europe. If 95% of popular apps stay on the App Store, then there will continue to be no appetite for change in the US.

But if suddenly Europe is getting different, better apps than Americans are, there might be popular demand to change things. But in that case it's still easier to see Apple making the changes out of public demand, rather than US legislation.

The most likely change in the US I would expect is Apple deciding to let Chrome and Firefox distribute their own browser engines in the US, if Chrome with a Chrome engine becomes popular in Europe and provides a lot of features Safari doesn't.

My take is this will follow in the US IF a few large states make rulings on this and higher courts decline to hear appeals. Ex. GDPR -> CCPA -> most companies just did compliance anyway for the US because of California's size

The problem with the US, and we're already seeing it play out with things like CCPA (California's GDPR-like privacy legislation), is that it is difficult to get momentum and bi-partisan support for sweeping changes in Congress. It either is watered down or gets deadlocked, so you end up in a situation where you have patchwork legislation, often conflicting in scope, state-by-state. I wouldn't expect much to change in the short to medium term.