Fan boy here, ready to answer this one.
1) If this was limited to devices not made by Google "AKA the Pixel". I would be OK with it. As different manufacturers should (as they already do and or can) offer alternative stores.
2) If this means that it would include the Pixel, I would be against it. As that is a Google made device. And as a consumer, you don't have to purchase a Pixel.
3) As for Apple, no. I still don't think it would be right to force Apple to open up. They built a closed system, and it got popular on its own merits. They are not a monopoly in the trustiest of definitions. They built their device, you don't have to buy it, and you have options. Due to the existence of Google Android AND multiple different vendors selling Android phones. Everyone has a choice to either be in or out of the Apple, Google, or Android 3rd Party handset ecosystem.
If anyone doesn't like the rules Apple has put in place. You're free to purchase one of many other Android devices. And if you don't trust any of those other manufactures for some reason or another. You can pick up a Pixel and have Android and "safety" too. If you like Apple, you can purchase any of the models they offer and have a seamless experience across Apple's ecosystem. So on and so forth.
And it is still possible for Microsoft or "other" company to create a mobile device and OS to compete with them too.
It's not anyones fault but their own why they couldn't and or sucked at it.