Its really easy to make a custom rom but hard to do serious "real life" stuff; companies don't want to make it easy. To most regular users, if they cant download apps from the google play store, and they can't use venmo\cashapp, then the OS is dead in the water from day 1
Trying to get some scale, you're hypothesizing about giving 10 millions to HSBC to make business with your startup, when they're throwing away 500+ millions every year just to cover their money laundering.
https://www.investopedia.com/stock-analysis/2013/investing-n...
And we're discussing doing this for basically every major banks.
I see it akin to the proverbial "not getting out of bed for less than XXXXX". You're getting out of bed every day, for free. But having someone make you do it for a specific reason will be an exponentially harder proposition.
> 1 line in their app
Aren't you asking them to maintain compatibility outside of Play Services and be on available on your platform ? That's a whole project, including their (or their contracting shop's) validating the whole new stack from a security and technical perspective, and a legal and business check on what that actually means to them.
Perhaps we can look at it from a darker perspective: if a random guy came to the bank to ask them support for their parralel phone ecosystem, the bank would at least want to know what they're getting into and what's in it for them. Especially if they're offered 10 millions for allegedly one line of code.
I just made up the figure. Perhaps 10 billion dollars is more enticing. Perhaps you have to purchase the company outright and then dictate they add support. My point is that it's not impossible to get the apps people need to work on an alternate Android OS. It is a matter of funding conpatibility. You can find a niche audience of people to start out with to make a competitive OS for them. And then overtime expand that audience more and more.
>Aren't you asking them to maintain compatibility
Typically the complaints about banks is that they use the Play Integrity library which doesn't trust other operating systems. So the ask is to support the Android API for integrity and to trust the key of the OS provider. This would be done via a new library to make integration easier and more foolproof.