Secondly, this is such an easy way to increase your take by 20+% that I would imagine almost every publisher is going to be offering their own payments platform, not just the biggest ones like Epic.
Stripe ( and others) have products right from incorporation (Atlas?), identity verification, custom reporting, fraud/risk, Charge backs, Tax reporting/ filing and even PoS terminals etc.
Most businesses have to deal with multiple channels (Android, web, iOS and others), custom reporting, and different risk/compliance will need solutions well beyond what Apple is offering
If new laws/regulations are made which are clear about this, then potentially very soon.
For such thinks sadly "making more clear laws" is sometimes faster then "enforcing not fully clear laws".
Even if the Epic lawsuit goes completely off the rails and Apple is forced to allow external app stores on iOS, they can still maintain a profitable app store if they provide the best experience to end users. Building an app store is very hard, and convincing people to install an alternative store is even harder, so I doubt they'll lose much there.
The app store is so ludicrously profitable that the exclusivity they enjoy can't possibly be the only reason it's making them money. This cut into Apple's (and Google's) profits, but it certainly won't mean the end of app stores as we know them.
I don't think they can. Their DNA on this evolved as a monopoly. They won't be able to compete, they will be slow and boring while clever people will overpower them.
My grandma isn't going to use any alternative store, she probably doesn't even understand the concept of different app stores. I think Apple will be fine, at least until competitors somehow gain a MASSIVE usability advantage.
It doesn't kill it much more then it killed the android store in the past when it wasn't (roughly, in practice) enforcing the same thing.
It's a revenue cut, but at least for the beginning it won't be a problem at all for apple, this might change at some point, but stocks have no reason to majorly drop now they still can do so in the future if it makes sense.
Google drive and Dropbox didn’t kill iCloud.
Apple can and will still reject any apps they feel like.
Apple now cannot reject apps because they have "Buy" links that redirect users elsewhere. And that's still a big deal.