Not sure all developers win if Apple changes its contract terms to require a cut of all sales, on or off the app store.
That would seem to then open up Apple to a new lawsuit.
"While the Court has found that evidence suggests Apple’s 30% rate of commission appears inflated, and is potentially anticompetitive, Epic Games did not challenge the rate. Rather, Epic Games challenged the imposition of any commission whatsoever. Nor did plaintiff show either that the provision of the DPLA which required developers."
So if evidence already suggests that Apple's commission is inflated, it only becomes more so when you still pay the commission, but no longer receive the services and benefits of Apple's IAP. Apple would then open themselves up to accusations of rent seeking, as those opting out of using Apple's IAP pay the same rates as those opting in.
Epic's mistake here appears to be attempting to get a free ride rather than pay a reasonable price for the ride.
Additionally, nothing indicates would Apple be entitled to a cut of purchases made outside of the app. Here's the relevant excerpt.
"The Court also notes that in the but-for world where developers could use an alternative processor, Apple would still be contractually entitled to its commission on any
purchase made within apps distributed on the App Store."
This would be no different than Netflix and Spotify not giving Apple a cut for purchases not made in the app. Apple is now being forced to treat all apps like they were only allowing "reader" apps to be treated.