If Apple allowed other payment methods, that would incentivize developers not to go through Apple at all. Even paid apps would switch over to an unlock model in order to avoid the 30% cut.
So I think it's very unlikely that Apple will allow other payment options. It's more likely for their 30% to go down, but even that's questionable.
I said you cannot bypass the 30% cut on the Google Play Store. Hosting your app elsewhere is not the same thing as hosting it on the Google Play Store.
Near as I can tell, it actually depends on what you're buying. If it's for the app itself, like an upgrade to "premium" or stuff for the game you're playing, it has to go through Google Pay and they take their cut. If it's something unrelated to the app, like a physical product or digital content for use outside the app, you're not beholden to Google Pay. But it seems like there are some grey areas.
I didn't get this from any single source, just bits and pieces put together from random forum posts and a few quora threads. And of course policies can change, so anything I found might be different right now. But I know you can buy digital books through Amazon's Kindle app on Android and it doesn't look like Google gets any of that cut: it's the normal "one click" purchase option you see in their web site, no prompt for Google Pay, just click and it's yours, downloading right away.
They can do something like Sign in with apple. If you are offering an alternative payment option, there should be an apple payment option too. If they are forced to do that Apple probably won't allow different pricing for it too.
I would be satisfied if they would allow you to charge a premium to use IAP instead of forcing all pricing to be the same (even though they take a big cut of the IAP).
So I think it's very unlikely that Apple will allow other payment options. It's more likely for their 30% to go down, but even that's questionable.