I seems to me like every company hopes that the new EU rules will open up the market and make them a ton of money. I, for one, doubt that the users will be so tech savvy and, quite the opposite, will get scared by the "jungle" of third party app stores, sideloading, links for purchases outside the App Store that they will voluntarily stay inside Apple's App Store. Too much choice creates insecurity. And, in the end, all these companies that operate outside the App Store will be pressured by the investors to come back to it. It seems to me the EU is listening to all the companies a lot and less to the users. Look at what happened with GDPR with every site opening with a pop-up. 90% of users blindly click "accept" to everything just because that screen is a pain. 5% of users have some browser plug-in installed that does the job for them, and 5% of users use basically only the Apps for everything and never see such a screen.
Imagine a future where I have to click on a link, go to a browser and give all my information to Spotify just to subscribe. Then I'll have to go to a separate App Store to download Word, Power Point and excel, and then go to a website to side load a utility.
And then, from time to time, I'll have to update everything. Opening up 2 App stores, 2 websites...
You can be sure people will use the same password for everything and then, once it gets stolen from the weakest link in the chain your information is no longer secure.
To sum up: I think these rules will only add confusion for users and, in the end, they will choose to stay on the beaten path (at least 80% of them) and, maybe, instead of Spotify which is no longer on the App Store, they will download Tidal, or Apple Music or something else that will be heavily promoted because Apple doesn't have an incentive to promote apps that don't generate revenue whatsoever.