[nitrogen]

The problem I see is that distributed collective action, like a bunch of people all choosing to support one contender against the duopoly, isn't achievable by the open source ecosystem. It's fragmentary by design and by personality. So there are a lot of things you "can" do, but no turn-key solution I can buy from a store or download from GitLab.

The other problem is that you have to choose between hardware quality and customization, because hardware is locked down and there isn't enough economic air left in the room for a third player to be able to invest enough to compete.

As for not looking much different from Android, the key difference would be where the control lies, and what the mindset is around control. You should have a robust code signing and containerization/permissions system, but those should be in the hands of users. With Android every single app installs with permission to portscan every network you connect it to. You will have an app store, but the user will come first, not the ad network.