This is the risk of "trusted computing" architectures. Who is governing the "trusted" part of that.
These cryptographic signatures are not as much of a death knell for Android as some would have you believe. The trick is to get a common code signing cert into your device, that is then used to sign any third party APK you want to run. You can avoid the Google tax this way. I assume that's how most sideloading sites and apps are going to handle this.
The question is, how do you add that certificate? Is it easy and straight forward (with plenty of scary warnings), as a user? Or is it going to be a developer options deal? Or will I need root to add the cert?
I'm not sure what that answer is right now.
I just want to finish this post with a few words about trusted computing models. Plainly: Apple has been doing this for years ... That's why you download basically everything from an app store with Apple. Whether on your Mac OS device, your iPhone, iPad or whatever iDevice.... Whether the devs need to sign it, or the app gets signed when it lands on the store, there's a signature to ensure that the app hasn't been tampered with and that Apple has given the app it's security blessings, that it is safe to run. Microsoft and Google have both been climbing towards the same forever. Apple embedded their root of trust in their own proprietary TPM which has been included with every Mac, and iDevice for a long ass time. Google also has a TPM, the Titan security module, I believe that was introduced around pixel 3? Or 4?... Microsoft made huge waves requiring it for Windows 11, and we all know what that discussion looks like. Apple requires a TPM (which they supply, so nobody noticed), Google has been adding a TPM and TPM functionality to their phones for years, and now Windows is the same. None of this is a bad thing. Trusted computing can eliminate much of the need for antivirus software, among other things. I digress. We've been going this way for a long time. Google is just more or less, doing what Apple has already done, and what Microsoft will very likely do very soon, making it a requirement. Battlefield 6 I think, was one of the first to require trusted computing on Windows and it will, for damned sure, not be the last that does. The only real hurdle here is managing what is trusted. So far, each vendor has kept the keys to their own kingdoms, but this is contrary to computing concepts. Like the Internet, it should be able to be done without needing trust from a specific provider. That's how SSL works, that's how the Internet works, that's how trusted computing should work. The only thing that should be secret is the private signing keys. What Google, Apple, and Microsoft should be doing, is issuing intermediary keys that can sign code signing certs. So trusted institutions that create apps, like... Idk, valve as an example, can create a signature key for steam and sign Steam with it, so the trust goes from MS root to intermediary key for valve, to steam code signing key, and suddenly you have an app that's trusted. Valve can then use their key to sign software on their store that may not have a coffee signing key of it's own. This is just one example based on Windows. And above all of this, the user should be able to import a trusted code signing cert, or an intermediary cert signing cert, to their service as trusted.
Anyways, thanks for coming to my Ted talk.