"Can you or someone actually make a list out of things that users will gain from all of this...?"
As usual here, you don't understand where the EU Commission is coming from. For them it is always about economics, its about opening competition for some players in some segments under some conditions. In this case its about dismantling the walled garden. Its about giving vendors (not just developers, though that may be a first step) the ability to sell apps to iPhone users. It is about making the application market for smart phones work in a similar way to that for the desktop or laptop PC.
People, particularly Apple fans, may not like this, they may not want it for themselves, they may also be very happy with the walled garden and positively like that it exists for everyone, they may like it because they think its good for Apple, but all that is immaterial to the EU. The EU wants to see competition for the Apple app store, so its going to, step by step, ensure that other suppliers can sell apps to iPhone users.
It isn't at all interested in whether, right now, the iPhone users want this. Its not interested in users. Its interested in markets and company power in them.
It has almost unlimited powers to bring about what it wants. It can give itself whatever legal powers it wants, it can issue orders and assign financial penalties to them which will give even a company the size of Apple very serious problems. As you would have seen, had you been following the recent EU legislation on this.
What we will now see is efforts by Apple to implement the letter of the regulation, but in such a way as to try and make sure that the alternative suppliers get as little as possible share. The EU will progressively slap down every measure Apple takes to enforce this. In this contest between a government the size of the EU and a company, no matter how large, the smart money is on the government.
If you want to understand the EU, its Bismarck's Zollverein updated. It has its earlier roots in Colbert. Competition internally, tariff and regulatory barriers externally. Rigorous enforcement of the rules on foreign entrants, less so for local players. When, through some accident of technology or innovation, you find yourself with a foreign player with dominant share of an important market segment, you get to work. The whole apparatus then focuses on how to clip its wings.
You all never heard of the Zollverein, and when you look it up, cannot see what that has to do with anything.
No, I guess not.