integrating with the legacy financial system will have the larger impact at scale.

The "not your keys not your coins" non-custodial dogma is for those on the privelged side of the digital divide and ignores most of those in the global south. The vast majority of those introduced to bitcoin, or onboarding, is from a fiat onramp and to a custodial wallet. Over time the user will want to learn more / technically proper ways of managing their sats, but shouldn't be shamed for not understanding it all on day 1.

FWIW: Apple and Google play stores are legacy systems and surveillance choke points, I would avoid those everywhere possible. To me, it's irresponsible to ever endorse someone use either of these, if you want to build a privacy centric future and care about the personal information of your users.

I speculate you've chosen this path of legacy system adoption for larger impact at scale than a PWA solution (which I've requested from day 1 as you know).