woud it apply on existing iphones or only new ones?

My guess would be all.

They have until March 2024 to comply or risk having fines based on global revenue, which they will not let happen. I think realistically we are looking at Dec/Jan.

Edit: correct year

It will likely apply to a specific version of the phone’s OS. And any device that can run that version will have the capability.

More broadly, you are talking about sideloading. And yes, the code is likely already there for Apple to implement this. They are just waiting on the ruling and their day in court to oppose. It’ll be big.

It may be gated by EU initially, but it honestly won’t take long for the world to follow suit.

I think Apple has said that they will only do this in the eu

It used to be that to install the Dev version of an app you had to pay the $99 Dev fee (basically you would copy that app as if you made it yourself )

Now you can install it for free, although there are still hoops to jump through.

I might be wrong, but I think those regulations will only become law in 2027.

I would guess that it could legally only apply to new phones from that date, but I don't think Apple or Google will split their ecosystem in two.